LIGHTNING PROTECTION SYSTEM EVALUATION BASED ON IMPEDANCE ANALYSIS

Abstract

A lightning protection system is provided, in particular for a rotor blade, the system including: i) a lightning conductor for conducting electrical energy of a lightning; and ii) a measurement device electrically coupled to the lightning conductor and configured to measure an impedance with respect to the lightning conductor. Further, a rotor blade and a wind turbine are provided.

Claims

1. A lightning protection system, for a rotor blade, comprising: a lightning conductor for conducting electrical energy of a lightning: and a measurement device electrically coupled to the lightning conductor and configured to measure an impedance with respect to the lightning conductor.

2. The lightning protection system according to claim 1, further comprising: an evaluation device configured to evaluate the lightning protection system, to determine a quality criterion, based on the impedance.

3. The lightning protection system according to claim 1, wherein the measurement device is, for measuring the impedance, further configured to provide an alternating current, AC, load to the lightning conductor, and sweep the AC load over a plurality of frequencies.

4. The lightning protection system according to claim 1, wherein the measurement device is, for measuring the impedance, further configured to perform a time domain based measurement.

5. The lightning protection system according to claim 1, further comprising: at least one conductor element electrically coupled to the lightning conductor and/or the measurement device; wherein the measurement device is further configured to measure an impedance of at least a part of the at least one conductor element.

6. The lightning protection system according to claim 5, wherein the lightning conductor and the at least one conductor element, are electrically connected in parallel.

7. The lightning protection system according to claim 1, wherein the measurement device comprises a first electrical connector and a second electrical connector, and wherein both the first electrical connector and the second electrical connector are connected to the lighting conductor or to an at least one conductor element.

8. The lightning protection system according to claim 1, wherein the measurement device comprises a first electrical connector and a second electrical connector, wherein the first electrical connector is connected to at least one conductor element, and wherein the second electrical connector is connected to the lighting conductor.

9. The lightning protection system according to claim 1, wherein the lighting conductor is configured as one of a cable, a rod, a bar; and/or wherein the system further comprises a spar cap which comprises or consists of an at least one conductor element.

10. A rotor blade comprising a lightning protection system according to claim 1.

11. A wind turbine comprising: a tower; and a wind rotor is arranged at a top portion of the tower, and which comprises at least one blade according to claim 10.

12. A method of evaluating a lightning protection system, according to claim 1, the method comprising: measuring an impedance with respect to a lightning conductor of the lighting protection system; and evaluating the lightning protection system based on the impedance.

13. The method according to claim 12, further comprising: mounting the evaluated lightning protection system, within a rotor blade, to a device to be protected.

14. A method comprising: utilizing an impedance analysis of a conductor to evaluate a lightning protection system of a rotor blade.

15. A method comprising: utilizing an impedance analysis of a conductor of a lightning protection system to evaluate a rotor blade construction.

Description

BRIEF DESCRIPTION

[0053] Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

[0054] FIG. 1 shows a lighting protection system for a rotor blade in accordance with an exemplary embodiment of the present invention;

[0055] FIG. 2 shows a lighting protection system for a rotor blade, in accordance with an exemplary embodiment of the present invention;

[0056] FIG. 3 shows a lighting protection system for a rotor blade, in accordance with an exemplary embodiment of the present invention;

[0057] FIG. 4 shows a lighting protection system for a rotor blade, in accordance with an exemplary embodiment of the present invention;

[0058] FIG. 5 shows a diagram to illustrate an impedance measurement, in accordance with an exemplary embodiment of the present invention;

[0059] FIG. 6 shows a diagram to illustrate an impedance measurement, in accordance with an exemplary embodiment of the present invention;

[0060] FIG. 7 illustrates an electric connection in a lighting protection system according to an exemplary embodiment of the present invention;

[0061] FIG. 8 shows a conventional example of a lighting protection system; and

[0062] FIG. 9 shows a wind turbine in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0063] The illustration in the drawing is schematic. It is noted that in different figures, similar or identical elements or features are provided with the same reference signs or with reference signs, which are different from the corresponding reference signs only within the first digit. In order to avoid unnecessary repetitions elements or features which have already been elucidated with respect to a previously described embodiment are not elucidated again at a later position of the description.

[0064] Further, spatially relative terms, such as front and back, above and below, left and right, et cetera are used to describe an element's relationship to another element(s) as illustrated in the figures. Thus, the spatially relative terms may apply to orientations in use which differ from the orientation depicted in the figures. Obviously, all such spatially relative terms refer to the orientation shown in the figures only for ease of description and are not necessarily limiting as an apparatus according to an embodiment of the invention can assume orientations different than those illustrated in the figures when in use.

[0065] According to an exemplary embodiment, the described impedance measurement system provides an advantage in determining if essential electrical components of the lightning protection system have been connected properly. With the results of resistance measurements, in contrast, it may not be conclusive if a satisfactory electrical connection exists between the electrically conductive elements (spar cap) and the blade lightning protection system. The same holds true for monitoring using the present method, where impedances of the lightning protection system are measured during the lifetime of the blade, to determine if the quality changes over time. Here, the impedance measurements would also provide an improved method for determining the quality of the lightning protection system during the lifetime of the blade, e.g. during full-scale blade structural test or full-scale testing of the lightning protection system according to the standards given in IEC 61400-24.

[0066] According to a further exemplary embodiment, the impact of the described solution is a new and effective method for determining the quality of wind turbine blade lightning protection system before, during, and/or after production of the blade and turbine, together with a possibility to do repetitive testing of the lightning protection quality during the entire lifetime of the blade. This solution could be applied towards testing the lightning protection system of wind turbine blades before they leave the production facilities, to ensure quality and homogeneous performance across the different blades.

[0067] According to a further exemplary embodiment, the described method could in principle be used to measure the impedance between any (two) points in the electrical system of a blade.

[0068] According to a further exemplary embodiment, the analysis of the conductor element(s) can be performed before connecting it with the rest of the lightning protection system. In that way the impedance analysis of the (separate) conductor elements can be done before connecting the elements, and when the result is compared to the analysis of the full system, additional knowledge of the impedance behavior can be obtained.

[0069] FIG. 1 shows a lighting protection system 100 for a rotor blade 114 according to an exemplary embodiment of the present invention. The rotor blade 114 is mounted via a blade adjustment device 116 to a rotor 111 of a wind turbine 101 (see FIG. 9). The blade 114 comprises along its direction of main extension, essentially from tip to root, a lighting conductor 110, for conducting electrical energy of a lightning strike. The lighting conductor 110 is made of metal and is configured e.g. as a cable, a rod, or a bar. The blade 114 further comprises spar caps 120 and 130, respectively arranged above and below the lighting conductor 110 in the blade 114. These spar caps 120, 130 comprise an electrically conductive material (and are thus conductor elements) and are electrically connected to the lighting conductor 110. The spar caps 120, 130 can for example comprise carbon reinforced polymer composites.

[0070] The lighting protection system 100 further comprises a measurement device 150 that is electrically connected via a first electric connection 151 and a second electric connection 152 to the lightning conductor 110 (at the tip and at the root). The measurement device 150 is configured to provide, through the electric connections 151, 152, an alternating current (AC) load (e.g. a voltage or a current) to the lightning conductor 110. Hereby, the measurement device 150 sweeps the AC load over a plurality of frequencies, and measure the corresponding impedance with respect to the lightning conductor 110. The measurement device 150 is further configured to provide the AC load (and frequency sweep) also to the conductor elements 120, 130. The lightning conductor 110 and the conductor elements 120, 130 are electrically connected in parallel. In another example, the impedance is measured using a time domain reflectometry-based method.

[0071] The lightning protection system 100 further comprises an evaluation device, that can be realized together with the measurement device 150, and that is configured to evaluate the lightning protection system 100 using an impedance analysis (of the impedance measurement). Such an evaluation may for example yield a quality criterion (e.g. functionality is fine, connection is fine, construction is fine) for the lightning protection system 100.

[0072] FIG. 2 shows a lighting protection system 100 for a rotor blade 114 according to another exemplary embodiment of the present invention. The design is very similar to FIG. 1 with the difference that the first electric connection 151 of the measurement device 150 is not directly connected to the lightning conductor 110, but to the upper spar cap 120 (a conductor element).

[0073] FIG. 3 shows a lighting protection system 100 for a rotor blade 114 according to another exemplary embodiment of the present invention. The design is very similar to FIG. 1 with the difference that both electrical connectors 151, 152 of the measurement device 150 are connected to two conductor elements 120, 130, respectively.

[0074] FIG. 4 shows a lighting protection system 100 for a rotor blade 114 according to another exemplary embodiment of the present invention. The design is very similar to FIG. 3 with the difference that both electrical connectors 151, 152 of the measurement device 150 are connected to only one conductor element 120. The conductor element 120 is further electrically coupled to the lighting conductor 110, so that the impedance of the latter can also be taken into account.

[0075] FIG. 5 shows a diagram to illustrate the impedance measurement/analysis according to an exemplary embodiment of the invention. The frequency F (see frequency sweep) is shown on the x-axis in Hertz (arbitrary values) and the corresponding impedance Z is shown in Ohm (arbitrary values) on the y-axis. Different results will be obtained, when measuring the impedance as follows (see FIG. 7 for the definition of the impedances): [0076] i) only for the lighting conductor 110 (Z2, see also FIG. 7), [0077] ii) for the lighting conductor 110 and one conductor element 120 in parallel (Z1, Z2), or [0078] iii) for the lighting conductor 110 and two conductor elements 120, 130 in parallel (Z1, Z2, Z3).

[0079] FIG. 6 shows a diagram to illustrate the impedance measurement/analysis according to another exemplary embodiment of the invention. The diagram is similar to FIG. 5, but, for comparison, a conventional resistance measurement is shown (see FIG. 8 for the definition of the resistors). Due to the applied direct current (constant frequency), there is no change in the frequency. Accordingly, the amount of information obtained by the conventional resistance measurement is much lower than the amount of information obtained by the described impedance measurement. In other words, FIG. 6 shows the comparison between the resistance and impedance at different frequencies when the inductive effects of the conductors are either included or omitted.

[0080] In particular with increasing frequencies, the difference in impedance increases, making it possible to detect e.g. if an electrically conductive spar cap is not (properly) electrically connected with the rest of the lightning protection system.

[0081] FIG. 7 shows the electric connection in a lightning protection system 110 according to another exemplary embodiment of the invention. This simplification shows the lighting conductor 110 and the two (or more) electrically conductive spar caps 120, 130 as three series impedances (the coils L1-L3 are only shown to represent impedances in general). The resistances and inductances follow the relations R1R3, L1L3, R1>R2 and L1<L2. Such a lightning protection system 110 has been applied, when measuring the results shown in FIGS. 5 and 6 above.

[0082] FIG. 9 shows a wind turbine 101 according to an exemplary embodiment of the invention. The wind turbine 101 comprises a tower 123 which is mounted on a ground (with a not depicted support structure). The wind turbine 101 can be located either onshore or offshore.

[0083] On top of the tower 123 there is arranged a nacelle 122. In between the tower 123 and the nacelle 122 there is provided a yaw angle adjustment portion 121 which is capable of rotating the nacelle 122 around a non-depicted vertical axis being aligned with the longitudinal extension of the tower 123. By controlling the yaw angle adjustment portion 121 in an appropriate manner it can be made sure that during a normal operation of the wind turbine 101 the nacelle 122 is always properly aligned with the current wind direction.

[0084] The wind turbine 101 further comprises a wind rotor 111 having three blades 114. In the perspective of FIG. 9 only two blades 114 are visible. The rotor 111 is rotatable around a rotational axis 111a. The blades 114, which are mounted at a hub 112, extend radially with respect to the rotational axis 111a and rotate within the rotational plane 114a.

[0085] In between the hub 112 and a blade 114 there is respectively provided a blade pitch angle adjustment device 116 in order to adjust the blade pitch angle of each blade 114 by rotating the respective blade 114 around an axis being aligned substantially parallel with the longitudinal extension of the respective blade 114. By controlling the blade pitch angle adjustment device 116, the blade pitch angle of the respective blade 114 can be adjusted in such a manner that, at least when the wind is not too strong, a maximum wind power can be retrieved from the available mechanical power of the wind driving the wind rotor 111.

[0086] As can be seen from FIG. 9, within the nacelle 122 there is provided a gear box 124. The gear box 124 is used to convert the number of revolutions of the rotor 110 into a higher number of revolutions of a shaft 125, which is coupled in a known manner to an electromechanical transducer 140. The electromechanical transducer is a generator 140. At this point it is pointed out that the gear box 124 is optional and that the generator 140 may also be directly coupled to the rotor 111 by the shaft 125 without changing the numbers of revolutions. In this case the wind turbine is a so called Direct Drive (DD) wind turbine.

[0087] Further, a brake 126 is provided in order to safely stop the operation of the wind turbine 101 or the rotor 111 for instance in case of emergency.

[0088] The wind turbine 101 further comprises a control system for operating the wind turbine 101 in a highly efficient manner. Apart from controlling for instance the yaw angle adjustment device 121, the depicted control system is also used for adjusting the blade pitch angle of the rotor blades 114 using actuators 116 in an optimized manner.

[0089] Each of the blades 114 comprises a lighting protection system 100 (see FIGS. 1 to 7). The control system 153 of the wind turbine 101 includes or is coupled to a lighting protection measurement device 150 that is configured to measure impedances within the lighting protection system 100. The control system 153 of the wind turbine 101 further includes or is coupled to an evaluation device 150 that is configured to evaluate the lighting protection system 100 based on the impedance measurement (by impedance analysis). Measurement device and evaluation device 150 can be implanted within one and the same device.

[0090] Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0091] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.