Inspect the wind turbine blade

Abstract

A method for inspecting a wind turbine blade. The wind turbine blade includes an electrothermal heating element and a surface protection layer. The method includes: exposing a test point of the electrothermal heating element; contacting the test point to establish an electrical connection between the test point and a sensor; and electrically connecting the sensor to the surface protection layer. Operating the sensor to measure a resistance value indicative of the resistance between the test point and the surface protection layer. Analyzing the resistance value to determine the condition of the wind turbine blade. The present invention provides a method for inspecting a wind turbine blade that enables detection of damage or defects that are difficult to detect by visual inspection or conventional non-destructive testing techniques. For example, the resistance value can give an indication of the presence of an electrical short circuit between the heating element and the surface protection layer.

Description

Technical Field

[0001] The present invention relates to a wind turbine blade having an electrothermal heating element, and a method of inspecting such a wind turbine blade. Background Art

[0002] WO 2019 / 001657 discloses an electrothermal heating element for a wind turbine blade. The heating element includes a conductive resistive material; two active busbars for supplying power to the conductive resistive material; and at least one dummy busbar located on the conductive resistive material at a predetermined spacing between the two active busbars. Summary of the Invention

[0003] A first aspect of the present invention provides a method of inspecting a wind turbine blade, the wind turbine blade including an electrothermal heating element and a surface protection layer, the method comprising: exposing a test point of the electrothermal heating element; contacting the test point to establish an electrical connection between the test point and a sensor; electrically connecting the sensor to the surface protection layer; operating the sensor to measure a resistance value indicative of the resistance between the test point and the surface protection layer; and analyzing the resistance value to determine the condition of the wind turbine blade.

[0004] The present invention provides a method of inspecting a wind turbine blade that enables detection of damage or defects that are difficult to detect by visual inspection or conventional non-destructive testing techniques. For example, the resistance value can give an indication of the presence of an electrical short circuit between the heating element and the surface protection layer.

[0005] Optionally, a single resistance value can be obtained from a single test point only. In this case, the resistance value can be compared with a threshold value to indicate the presence or absence of an electrical short circuit. Alternatively, the method may include: exposing a plurality of test points of the electrothermal heating element; contacting the plurality of test points to establish electrical connections between the plurality of test points and the sensor; and operating the sensor to measure a plurality of resistance values, each resistance value indicative of the resistance between a corresponding one of the plurality of test points and the surface protection layer; and analyzing the resistance values to determine the condition of the wind turbine blade. For example, the analysis of the resistance values can indicate the approximate location of a suspected electrical short circuit.

[0006] The sensor may include a measuring probe, and the electrical connection can be established by contacting the plurality of test points one by one with the measuring probe. Alternatively, the sensor may have a plurality of measuring probes for establishing electrical connections simultaneously.

[0007] The condition of the wind turbine blade includes an estimated fault location, which is estimated based on the analysis of the resistance values and the locations of the plurality of test points.

[0008] Optionally, the step of analyzing the resistance values includes: identifying one or more of the lowest resistance values among the resistance values, and the condition of the wind turbine blade includes an estimated fault location that is estimated based on one or more positions of one or more test points associated with one or more of the lowest resistance values.

[0009] The wind turbine blade may include an electrical grounding network, and the electrical grounding network may include the surface protection layer and one or more sub-components. The sensor may be electrically connected to the surface protection layer by bringing one of the one or more sub-components or the surface protection layer into contact with a reference probe.

[0010] The electrothermal heating element may include an electrothermal heating pad.

[0011] The electrothermal heating pad may be made of a conductive resistive material, such as a carbon fiber shielding material.

[0012] The surface protection layer may include a perforated foil, a grid, or a grille.

[0013] The step of analyzing the resistance values to determine the condition of the wind turbine blade may include: analyzing one or more resistance values to detect the presence or absence of an electrical short circuit between the electrothermal heating element and the surface protection layer.

[0014] The surface protection layer may be a lightning protection layer.

[0015] The surface protection layer may be metallic, such as copper or aluminum.

[0016] The electrothermal heating element may include one or more busbars, wherein the (or each) test point is located on a corresponding one of the busbars.

[0017] The (or each) busbar may include connection pads on the busbar, wherein at least one of the test points is located on a corresponding one of the connection pads on the corresponding busbar of the busbars.

[0018] The sensor may include a measurement probe, and the (or each) electrical connection may be established by bringing the corresponding test point into contact with the measurement probe.

[0019] The wind turbine blade may further include an insulating layer located between the electrothermal heating element and the surface protection layer. The insulating layer may be made of any suitable electrically insulating material, such as a glass fiber composite material.

[0020] The test points of the electrothermal heating element can be exposed by removing blade materials such as a part of the insulating layer and a part of the surface protection layer. If there are multiple test points, each test point can be exposed by removing the corresponding part of the insulating layer and the corresponding part of the surface protection layer.

[0021] The aforesaid parts of the insulating layer and the surface protection layer can be removed by grinding.

[0022] The wind turbine blade can be repaired by replacing the removed parts of the insulating layer and the surface protection layer with repair patches.

[0023] Another aspect of the present invention provides a method for inspecting and repairing a wind turbine blade, the method comprising inspecting the wind turbine blade by the method of the first aspect, wherein the analysis of one or more resistance values yields the estimated fault location of the wind turbine blade; and replacing the part of the electrothermal heating element at the estimated fault location.

[0024] The wind turbine blade may further include an insulating layer located between the electrothermal heating element and the surface protection layer.

[0025] The method may further include replacing the parts of the electrothermal heating element, the surface protection layer and the insulating layer at the estimated fault location.

[0026] The electrothermal heating element may include two or more busbars, the two or more busbars including an adjacent pair of busbars, wherein the estimated fault location is located between the pair of busbars, and all the electrothermal heating elements between the pair of busbars are replaced.

[0027] A second aspect of the present invention provides a wind turbine blade, the wind turbine blade comprising: an electrothermal heating element; and a surface protection layer, wherein the electrothermal heating element includes: an electrothermal heating pad; two active busbars located on the electrothermal heating pad for supplying power to the electrothermal heating pad; at least one dummy busbar located on the electrothermal heating pad between the two active busbars; and connection pads located on each active busbar and each dummy busbar.

[0028] The connection pads can be located on the side of the busbar opposite to the surface protection layer, or on the side of the busbar the same as the surface protection layer.

[0029] The connection pads can be made of copper or any other conductive material.

[0030] Each connection pad can have a thickness greater than that of the busbar carrying the connection pad.

[0031] The electrothermal heating pad can be made of a conductive resistive material, such as a carbon fiber shielding material.

[0032] The surface protective layer can be made of a conductive material. For example, the surface protective layer can be metallic. Description of the Drawings

[0033] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0034] Figure 1 a wind turbine is shown;

[0035] Figure 2 a wind turbine blade having an electrothermal heating element is shown;

[0036] Figure 3 the electrothermal heating element is shown;

[0037] Figure 4 is a cross-sectional view through a portion of the blade;

[0038] Figure 5 a sensor connected to the surface protective layer and an electrical grounding network is shown;

[0039] Figure 6 is a cross-sectional view corresponding to after the blade has been tested and repaired Figure 4 ;

[0040] Figure 7 six resistance values are shown;

[0041] Figure 8 is a cross-sectional view corresponding to after the blade has been tested and the electrothermal heating element has been repaired Figure 4 ;

[0042] Figure 9 an alternative electrothermal heating element is shown;

[0043] Figure 10 is shown taken from Figure 9 three series of resistance values of the elements;

[0044] Figure 11 is a cross-sectional view through a portion of an alternative blade; and

[0045] Figure 12 a bus bar having a pair of connection plates is shown. Detailed Description

[0046] Figure 1The wind turbine 1 is shown. The wind turbine 1 has a tower 2 and a nacelle 3 located at the top of the tower 2. A wind turbine rotor 4 is connected to the nacelle 3 and is arranged to rotate relative to the nacelle 3. The wind turbine rotor 4 includes a wind turbine hub 5 and a plurality of wind turbine blades 6 extending from the hub 18. Although a wind turbine rotor 4 with three blades 4 is shown, different numbers of blades, such as two or four, can be used.

[0047] Each blade 6 has a row of electrothermal heating elements embedded along its leading edge. These heating elements can be used for one or both of anti-icing (preventing ice accumulation) or de-icing (removing ice accumulation) of the blade 6. Figure 2 A single heating element among these heating elements 10 is shown, and the other heating elements have been omitted from Figure 2 for clarity.

[0048] As Figure 3 and Figure 4 shown, the heating element 10 includes an electrothermal heating pad 24 made of a conductive resistive material, and one or more copper busbars 11 to 16 may be provided on the pad 24 and spaced apart along its length. The spacing between the busbars is typically on the order of 500 mm.

[0049] The pad 24 has a sheet resistance that is selected such that when a voltage is applied between the busbars 11, 16 at each end, the pad generates heat at a desired heat flux due to resistance or ohmic heating.

[0050] The pad 24 may comprise, for example, a carbon fiber shield, a carbon / glass fiber shield, or a metal grid.

[0051] The heating element 10 may have a length on the order of 8 m and a width on the order of 0.7 m, for example. Figure 3 Only six busbars are shown in the figure, but more busbars can be used in practice. For example, if the length is 8 m and the spacing is 500 mm, there will be seventeen busbars.

[0052] The busbars 11, 16 at each end are "active" busbars (since they are used to apply a voltage along the entire length of the heating element), while the other busbars 12 to 15 are "dummy" busbars that enable repair in a more efficient manner, as described in WO2019 / 001657, the content of which is incorporated herein by reference.

[0053] Figure 4 is a cross-sectional view through the blade at the location of the heating element 10. The main structure is a blade laminate 23 that may include, for example, a laminated composite material. The blade also has a surface protection layer 21 and an insulating layer 22 located between the electrothermal heating element 10 and the surface protection layer 21.

[0054] A wind turbine blade includes an electrical grounding network that includes a surface protection layer 21 and one or more other sub-components, such as a metal blade tip, a cable at the blade root, or a carbon spar cap. In Figure 4 and Figure 5 one of these sub-components is schematically shown at 27.

[0055] The surface protection layer 21 is made of a metallic material such as aluminum or copper. The purpose of the surface protection layer 21 is to protect the heating element 10 and the blade laminate 23 when the blade is struck by lightning. In a lightning strike event, the surface protection layer 21 conducts the current to the ground via the other sub-components of the electrical grounding network. Thus, the surface protection layer 21 serves as a lightning protection layer. The surface protection layer 21 typically includes a perforated foil, an expanded foil, a mesh, or a grille. In a preferred example, the surface protection layer 21 includes an aluminum expanded foil.

[0056] The insulating layer 22 may include one or more layers of a glass fiber composite material (e.g., glass fibers impregnated with resin). The purpose of the insulating layer 22 is to electrically isolate the heating element 10 from the surface protection layer 21.

[0057] The blade 6 may also have a surface coating 20 at its outer surface. The surface coating 20 may include, for example, a gel coat or a paint layer.

[0058] Figure 5 A method for inspecting a wind turbine blade is shown in

[0059] First, a test point of the electrothermal heating element 10 is exposed. In this example, the test point is located on one of the busbars 14, and the test point is exposed by the following steps: removing a portion of the surface coating 20 to leave a hole 20a, then removing a portion of the surface protection layer 21 to leave a hole 21a, and then removing a portion of the insulating layer 22 to leave a hole 22a. For example, these portions can be removed by grinding using a ball-end grinder. In this example, the holes 20a, 21a, 22a have gradually decreasing diameters.

[0060] If the test point is not covered by the insulating layer and the surface protection layer, the test point can be exposed by removing any other blade material covering it.

[0061] A sensor 25 (e.g., a digital multimeter) is equipped with a measurement probe 26 and a reference probe 28. An electrical connection is established with the test point on the busbar 14 by passing the measurement probe 26 through the pre-formed holes 20a, 21a, 22a and then contacting the test point (in this case, contacting the busbar 14).

[0062] The sensor 25 can be electrically connected to the surface protection layer 21 by bringing one of the surface protection layer 21 or other sub-components of the electrical grounding network into contact with the reference probe 28. In this example, the reference probe 28 contacts the sub-component 27, which can be, for example, a metal blade tip. For example, the reference probe 28 may include an "alligator clip" for attaching it to the metal blade tip.

[0063] Once the electrical connection is established as shown in Figure 5 , the sensor 25 is operated to measure the resistance value between the probes 26, 28, which indicates the resistance between the bus bar 14 and the surface protection layer 21.

[0064] If the blade is not damaged or otherwise malfunctioning, the resistance value will be very high, essentially infinite, due to the very high resistance of the insulating layer 22. If the blade is faulty (e.g., due to damage from lightning strikes, damage to the blade surface, or manufacturing faults), this can result in an electrical short circuit between the heating element 10 and the surface protection layer 21. Such short circuits may be small and difficult to detect by visual inspection or traditional non-destructive testing techniques.

[0065] The electrical short circuit will cause the resistance value to decrease. If the fault location (i.e., the location of the electrical short circuit) is close to the bus bar 14, the resistance will be very low, but if the fault location is far from the bus bar 14 (e.g., at the left-hand bus bar 11), the resistance will be higher but still much lower than in the non-fault case.

[0066] Therefore, the resistance value can be analyzed to determine the condition of the wind turbine blade. In the most basic case, the analysis can simply compare the resistance value with a threshold to detect the presence or absence of an electrical short circuit between the electrothermal heating element 10 and the surface protection layer 21. If the resistance value is higher than the threshold, it is determined that the blade is in a non-fault condition; if it is lower, it is determined that the blade is in a fault condition.

[0067] If it is determined that the blade is in a non-fault condition, the blade is repaired by replacing the removed portions of the surface coating 20, the surface protection layer 21, and the insulating layer 22 with the gel or coating 20b and the repair patches 21b, 22b shown in Figure 6 . The repair patch 22b can be laid as a dry fiberglass layer to be subsequently infused with resin, or it can be applied as a prepreg (fiberglass pre-impregnated with resin) to be subsequently cured.

[0068] If it is determined that the blade is in a fault condition based on only a single resistance value, the fault location can only be roughly estimated. Therefore, in a preferred method, multiple test points of the electrothermal heating element 10 are exposed and then tested in order to more precisely estimate the fault location.

[0069] In this preferred method, the test points can be brought into contact with the measurement probes 26 one by one to establish an electrical connection between the test points and the sensor. Alternatively, the sensor can have a plurality of measurement probes 26, each measurement probe contacting a corresponding one of these test points.

[0070] The sensor is operated to measure a plurality of resistance values, each resistance value indicating the resistance between a corresponding one of the test points and the surface protection layer 21. The reference sensor 28 remains connected to the electrical ground network during this process.

[0071] Figure 7 Six resistance values are indicated by crosses in the figure, each resistance value corresponding to a respective one of the bus bars 11 to 16. The resistance values are analyzed to identify one or more of the lowest resistance values among the resistance values. In this case, two lowest resistance values 30, 31 are identified. Then the fault location is estimated based on the positions of a pair of adjacent bus bars 14, 15 associated with these two resistance values 30, 31. The resistance values 30, 31 are very similar, so the fault location is estimated to be midway between the two bus bars 14, 15.

[0072] Alternatively, there may be a single resistance value that is much lower than all the other resistance values. In this case, the fault location is estimated to be on or near the bus bar associated with this resistance value.

[0073] Once the fault location is estimated as described above, the blade can be repaired as Figure 8 shown. First, the holes 20a, 21a, 22a are enlarged, for example by grinding, to expose a larger area of the electrothermal heating element. Then, the part of the electrothermal heating element at the estimated fault location is repaired. In this case, the estimated fault location is between two adjacent bus bars 14, 15, so all the carbon fiber shielding pads 24 between the bus bars 14, 15 are removed (e.g., by grinding) and replaced with carbon fiber shielding repair patches 24a. The repair patches 24a have inner-facing copper bus bars 14a, 15a that contact the outward-facing bus bars 14, 15.

[0074] Then the repair is completed by replacing the removed portions of the surface coating 20, the surface protection layer 21, and the insulation layer 22 with the gel or coating 20c and the repair patches 21c, 22c as Figure 8 shown. The repair patch 22c can be laid as a dry fiberglass layer to be subsequently infused with resin, or it can be applied as a prepreg (fiberglass pre-impregnated with resin) to be subsequently cured..

[0075] The above example assumes that a voltage difference is applied between the bus bars 11, 16 at the two ends, so in this case the lowest resistance value clearly identifies the fault location. Figure 9An alternative arrangement is shown. In this case, the same voltage is applied to the busbars 40, 44 at both ends via the high-voltage line 46, and the central busbar 42 is connected to the neutral voltage via the neutral connection 45.

[0076] The blade is damaged at three positions 47 to 49. The damage is greatest at position 47 and least at position 49. In the first test step, a first series of eleven resistance values is measured, each value corresponding to a respective busbar. This series is indicated by the lower line in Figure 10 and has three low points. Two low points 47a are associated with a pair of adjacent busbar pairs 40, 41 on either side of the fault location 47. The third low point 47b is associated with the busbar 44 at the opposite end of the heating element. The low point 47a is slightly lower than the low point 47b, so the heating element is repaired between the busbars 40, 41.

[0077] Before the blade is fully repaired, in the second test step, a second series of eleven resistance values is measured, each value corresponding to a respective busbar. This series is indicated by the middle line in Figure 10 and has two low points 48a associated with a pair of adjacent busbars on either side of the fault location 48, so the heating element is repaired between these busbars. Note that the average resistance is higher than the average resistance of the first series.

[0078] In the third test step, a third series of eleven resistance values is measured, each value corresponding to a respective busbar. This series is indicated by the top line in Figure 10 and has two low points 49a associated with a pair of adjacent busbars on either side of the fault location 49, so the heating element is repaired between these busbars. Note that the average resistance is higher than the resistance of the first series and the second series.

[0079] In the fourth test step, a single resistance value indicating a very high or infinite resistance is measured because all necessary repairs to the heating element 10 have now been made. Then a repair patch and gel / paint are applied to complete the repair.

[0080] Figure 11 is a cross-sectional view through a wind turbine blade according to an embodiment of the present invention. The wind turbine blade has many features in common with the Figures 1 to 8 wind turbine blade, and the same reference numerals are used for equivalent components. The blade has a blade laminate 23, an electrothermal heating element 10a, a surface protection layer 21, an insulating layer 22 located between the electrothermal heating element 10a and the surface protection layer 21; and a surface coating 20.

[0081] The electrothermal heating element 10a includes: an electrothermal heating pad 24; two active busbars 50a located on the electrothermal heating pad 24 for supplying power to the electrothermal heating pad 24; and a dummy busbar 50 located on the electrothermal heating pad between the two active busbars 50a. In this case, for ease of illustration, only a single dummy busbar 50 is shown, but the number will typically be greater, for example as Figure 3 and Figure 10 shown.

[0082] Connection pads 51a are provided on the lower side of each active busbar 50a, and connection pads 51 are provided on the lower side of each dummy busbar 50. The connection pads 51, 51a can be made of the same material (such as copper) as the busbars 50, 50a carrying them or another conductive material. The connection pads 51, 51a are electrically connected to the busbars 50, 50a carrying them.

[0083] The busbars 50, 50a are very thin, and the connection pads 51, 51a are much thicker than the busbars (note that Figure 11 not drawn to scale). Each connection pad can have a thickness of no more than 2 mm.

[0084] The connection pads 51, 51a ensure that when the blade is grounded for connection to the busbar, as Figure 11 shown, for the dummy busbar 50, the busbar is not grounded due to the connection pad.

[0085] In this example, the connection pads 51, 51a are located on the lower side of the busbar (i.e., the side opposite to the surface protective layer 21), but they can also be located on the top of the busbar (i.e., the same side as the surface protective layer 21).

[0086] Figure 12 The shape and position of the connection pad 51 on the dummy busbar are shown. In this case, the connection pad 51 is square and is positioned at a known distance D from the end of the busbar such that it is located at a known position relative to the leading edge of the blade. The connection pads 51a on the active busbars are similar and are positioned at the same points along the length of their respective busbars.

[0087] Figure 12 A connection pad 52 with an alternative (circular) shape is also shown. Note that this is only for illustrative purposes: each busbar has only a single connection pad.

[0088] Although the present invention has been described above with reference to one or more preferred embodiments, it should be understood that various changes or modifications can be made without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A method for inspecting a wind turbine blade, the wind turbine blade comprising an electrothermal heating element and a surface protection layer, the method comprising: Exposing a test point of the electrothermal heating element; Contacting the test point to establish an electrical connection between the test point and a sensor; Electrically connecting the sensor to the surface protection layer; Operating the sensor to measure a resistance value indicative of the resistance between the test point and the surface protection layer; And Analyzing the resistance value to determine the condition of the wind turbine blade.

2. The method according to claim 1, the method comprising: Exposing a plurality of test points of the electrothermal heating element; Contacting the plurality of test points to establish an electrical connection between the plurality of test points and the sensor; And operating the sensor to measure a plurality of resistance values, each resistance value indicative of the resistance between a corresponding one of the plurality of test points and the surface protection layer; and analyzing the resistance values to determine the condition of the wind turbine blade.

3. The method according to claim 2, wherein, The sensor includes a measuring probe, and the electrical connection is established by contacting the plurality of test points one by one with the measuring probe.

4. The method according to claim 2 or 3, wherein The condition of the wind turbine blade includes an estimated fault location, which is estimated based on the analysis of the resistance values and the positions of the plurality of test points.

5. The method according to claim 2 or 3, wherein The step of analyzing the resistance values includes: identifying one or more of the lowest resistance values among the resistance values, and the condition of the wind turbine blade includes an estimated fault location, which is estimated based on the one or more positions of one or more of the test points associated with the one or more lowest resistance values among the resistance values.

6. The method according to any one of claims 1 to 3, wherein The wind turbine blade includes an electrical grounding network, the electrical grounding network including the surface protection layer and one or more sub-components; and the sensor is electrically connected to the surface protection layer by contacting one of the one or more sub-components or the surface protection layer with a reference probe.

7. The method according to claim 6, wherein The sensor is electrically connected to the surface protection layer by contacting one of the one or more sub-components with a reference probe.

8. The method according to any one of claims 1 to 3, wherein The sensor is electrically connected to the surface protection layer by contacting the surface protection layer with a reference probe.

9. The method according to any one of claims 1 to 3, wherein The electrothermal heating element includes an electrothermal heating pad.

10. The method according to any one of claims 1 to 3, wherein The surface protection layer includes a perforated foil, a grid or a grille.

11. The method according to any one of claims 1 to 3, wherein The step of analyzing the resistance values to determine the condition of the wind turbine blade includes: analyzing one or more resistance values to detect the presence or absence of an electrical short circuit between the electrothermal heating element and the surface protection layer.

12. The method according to any one of claims 1 to 3, wherein The surface protection layer is a lightning strike protection layer.

13. The method according to any one of claims 1 to 3, wherein, The surface protection layer is metallic.

14. The method according to any one of claims 1 to 3, wherein, The electrothermal heating element includes one or more busbars, and each test point is located on a corresponding one of the one or more busbars.

15. The method according to any one of claims 1 to 3, wherein The sensor includes a measuring probe, and each electrical connection is established by contacting a corresponding test point with the measuring probe.

16. The method according to any one of claims 1 to 3, wherein The wind turbine blade further includes an insulating layer located between the electrothermal heating element and the surface protection layer; and wherein test points of the electrothermal heating element are exposed by removing a part of the insulating layer and a part of the surface protection layer, or respective test points are exposed by removing corresponding parts of the insulating layer and the surface protection layer.

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