DAMAGE ASSESSMENT ARRANGEMENT

Abstract

A damage assessment arrangement for assessing the extent of damage to a lightning receptor electrically connected to a down conductor of a wind turbine rotor blade includes a measurement pulse module including a pulse generator arranged to transmit a pulse into one end of the down conductor and a return signal detector arranged to detect the return signal; a return signal analysis module configured to determine the extent of alteration of the return signal relative to an expected return signal; and a damage estimation module configured to relate the relative extent of alteration to a measure of damage to rotor blade LPS. The following further describes a wind turbine with such a damage assessment arrangement; and a method of assessing the extent of damage to a rotor blade LPS.

Claims

1. A damage assessment arrangement for assessing the extent of damage to a lightning receptor electrically connected to a down conductor of a wind turbine rotor blade, which damage assessment arrangement comprises a measurement pulse module comprising a pulse generator arranged to transmit a pulse into one end of the down conductor and a return signal detector arranged to detect the return signal; a return signal analysis module configured to determine the extent of alteration of the return signal relative to an expected return signal; and a damage estimation module configured to relate the relative extent of alteration to a measure of damage to a receptor.

2. The damage assessment arrangement according to claim 1, wherein the pulse analysis module is configured to quantify the time delay of the return signal relative to the expected return signal.

3. The damage assessment arrangement according to claim 1, wherein the pulse analysis module is configured to quantify the attenuation of the return signal relative to the expected return signal.

4. The damage assessment arrangement according to claim 1, the pulse analysis module is configured to quantify the distortion of the return signal relative to the expected return signal.

5. The damage assessment arrangement according to claim 1, wherein an assessment of damage to a receptor is made on the basis of the time delay and/or the attenuation and/or the distortion of the return signal.

6. The damage assessment arrangement according to claim 1, wherein an assessment of damage to the down conductor is made on the basis of time delay and/or attenuation and/or distortion of the return signal.

7. The damage assessment arrangement according to claim 1, comprising a look-up table relating values of time delay and/or attenuation and/or distortion to measures of damage to a receptor type.

8. A wind turbine comprising a plurality of rotor blades, wherein each rotor blade comprises a down conductor of a lightning protection system, and at least one lightning receptor arranged at the rotor blade exterior and electrically connected to the down conductor; and the damage assessment arrangement according to claim 1 for assessing the extent of damage to the receptors.

9. The wind turbine according to claim 8, wherein the measurement pulse module comprises a single pulse generator, and a return signal detector for each rotor blade down conductor.

10. The wind turbine according to claim 8, wherein the damage assessment unit is at least partially implemented at a location remote from the wind turbine.

11. A method of assessing the extent of damage to a lightning receptor electrically connected to a down conductor of a wind turbine rotor blade, which method comprises providing the damage assessment arrangement according to claim 1; operating the pulse generator of the measurement pulse module to transmit a pulse into one end of the lightning down conductor; operating the return signal detector of the measurement pulse module to detect the return signal; analyzing the return signal to determine the extent of alteration relative to an expected return signal; and relating the relative extent of alteration to a measure of damage to the receptors of that lightning down conductor.

12. A method of calibrating the damage assessment arrangement of claim 1, comprising the steps of A) providing, for each receptor position of a rotor blade down conductor, an undamaged receptor and a plurality of damaged receptors; B) selecting a set of receptors for connection to the receptor positions of the down conductor and quantifying the measure of damage of each receptor; C) connecting the receptors of the selected set to the receptor positions of the down conductor and operating the measurement pulse module to transmit a pulse into the down conductor and to record the return signal; relating the parameters of the return signal to the quantified measures of damage for the receptors; and D) repeating steps B and C for multiple combinations of damaged and undamaged receptors.

13. The method according to claim 12, comprising a step of compiling a look-up-table that relates the measure of damage of each receptor to the corresponding return signal.

14. The method according to claim 12, wherein a look-up-table is compiled for a specific receptor type and a specific down-conductor type.

15. The method according to claim 12, wherein the calibration procedure is performed multiple times, and each calibration procedure is performed for a distinct temperature range.

Description

BRIEF DESCRIPTION

[0031] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0032] FIG. 1 shows a conventional wind turbine;

[0033] FIG. 2 illustrates elements of a rotor blade LPS;

[0034] FIG. 3 is a schematic diagram showing exemplary signals; and

[0035] FIG. 4 shows a block diagram of an embodiment of the inventive damage assessment arrangement.

[0036] FIG. 1 shows a conventional wind turbine 2, which has an aerodynamic rotor comprising three rotor blades 20 mounted to a hub 21. A generator is housed in a nacelle 22, which is mounted atop a tower 23. A very simplified set of lightning down conductors 20C, 23C of the wind turbine's LPS is indicated for the purpose of illustration. The down conductors and other elements of the wind turbine LPS are generally arranged in interior cavities, in the tower wall, etc., as will be known to the skilled person. In a well-designed LPS, lightning current from a lightning strike to any part of the wind turbine will see an essentially direct path to ground.

[0037] FIG. 2 illustrates elements of an exemplary rotor blade LPS. The diagram shows the tip region of a rotor blade 20, a down conductor 20C arranged in the rotor blade interior, and multiple receptors 20R at various positions S1, S2, S3, S4. A tip-end receptor 20R at position S4 is shaped for mounting near the outermost tip end of the rotor blade 20 and connects electrically to the down conductor 20C. Several side receptors 20R at positions S1-S3 are shaped for mounting on the pressure side or suction side of the rotor blade and also connect electrically to the down conductor 20C, which may be assumed to be installed in the interior of the rotor blade 20. During the lifetime of the rotor blade, the receptors 20R can deteriorate as described above. Material evaporation along with any surface damage will manifest as distortion of a return signal (relative to an expected signal) when a pulse is transmitted into the down conductor.

[0038] This is illustrated in FIG. 3, which shows exemplary signal shapes. The drawing shows a Gaussian pulse P at the point of its transmission into the end of a down conductor 20C, and the shape of an expected return signal R.sub.E, i.e., shape of the return signal after reflection by undamaged elements of a pristine (new) rotor blade LPS. The diagram also shows several possible return signals R1, R2, R3 received after reflection by the rotor blade LPS.

[0039] A first reflected signal R1 has undergone only minor distortion relative to the expected return signal R.sub.E, so that the rotor blade LPS may be deemed to be healthy. The receptors 20R are each assigned an appropriate damage assessment level, for example: D.sub.good meaning “receptor is healthy”. A second reflected signal R2 has undergone minor distortion relative to the expected return signal R.sub.E, indicating that the receptors are functional but have sustained minor damage. Each receptor 20R is assigned an appropriate damage assessment level, for example: D.sub.mild meaning “receptor exhibits slight wear”. A third reflected signal R3 has undergone severe distortion relative to the expected return signal R.sub.E, indicating that at least one receptor may no longer be reliable. Analysis of the reflected signal R3 indicates that the receptor 20R at the third position S3 is no longer reliable, while the receptors at the other positions have sustained significant levels of wear. The receptors are assigned appropriate damage assessment levels, for example: D.sub.fail meaning “receptor fail” for the receptor at position S3; and D.sub.poor for the remaining receptors. This exemplary diagram indicates a time-domain representation of the return signals, but it shall be understood that the damage levels can be deduced from a time-domain and frequency-domain analysis of the return signal. Of course, these damage assessment levels are proposed only by way of example, and any number of damage assessment levels may be used to cover a broader range of “health states” for the rotor blade LPS receptors.

[0040] By collecting information in a calibration phase, using many instances of that receptor and down conductor arrangement, a look-up table (LUT) can be compiled to relate parameters of such return signals to receptor damage. The damage assessment levels described in the above example may be chosen by identifying a “best match” between the parameters of a reflected signal and the parameters of a LUT entry, as will be known to the skilled person.

[0041] FIG. 4 is a simplified schematic to illustrate the inventive damage assessment arrangement 1 installed in an operational wind turbine. The diagram shows a measurement pulse module comprising a pulse generator 10 and a return signal detector 11. The measurement pulse module 10, 11 is connected to the down conductor 20C of a rotor blade 20, for example by means of a 50Ω coaxial cable and a suitable connector. The pulse generator 10 is arranged to transmit a pulse P into the inner end 20C.sub.root of the lightning down conductor 20C. The return signal detector 11, for example a time-domain reflectometer and/or a digital sampling oscilloscope, is arranged to detect the reflected return signal R, and can be realized to report a time delay of the reflected return signal R and/or a magnitude of the reflected return signal R and/or the shape of the reflected return signal R. These parameters(s) 110 are recorded for each detected return signal R.

[0042] In this exemplary embodiment, the pulse generator 10 applies an electrical pulse P to the inner end 20C.sub.root of the lightning conductor 20C. The pulse P—for example a Gaussian pulse P—travels along the lightning conductor 20C in the direction of the tip. The pulse P will travel to the outer end of the down conductor 20C, where it is reflected. Any receptor 20R (e.g., at positions S1-S4 of FIG. 2) connected to the down conductor 20C will contribute in some way to the distortion of the pulse, which travels back to the inner end of the down conductor 20C where it is detected as the return signal R by the pulse detector 11. Of course, as will be known to the skilled person, the down conductor itself will also contribute to some extent to the distortion of the return signal R.

[0043] A receptor damage assessment unit 12 is configured to estimate the receptor health on the basis of the observed reflection parameters 110 recorded by the return signal detector 11. In a straightforward embodiment as indicated here, the observed reflection parameters 110 can be matched to the closest corresponding entry in a look-up table 120 as described above. For example, a set of return signal parameters 110 reported by the return signal detector 11 can be matched to a set of return signal parameters in the database 120, and the corresponding damage assessment level 12R can be identified and reported to an operator or controller, for example to a remote wind park operator 4. The operator can then decide whether a service schedule is necessary (e.g., the damage assessment level 12R is classified as “poor” or “fail”) or whether a service schedule is not necessary (e.g., the damage assessment level is classified as “good” or only “mild”).

[0044] Although the present invention has been disclosed in the form of preferred 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.

[0045] 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.