Improvements related to stray current detection in wind turbine generators

Abstract

A power generation assembly (20) for a wind turbine (1). The power generation assembly includes a gearbox (22) including a gearbox output shaft; a generator (24) including a rotor (32) coupled to the gearbox output shaft; and a current measurement module (40) located between the gearbox (22) and the generator (24). The current measurement module (40) includes an electrical pickup (42) mounted to the power generation assembly (20), wherein the electrical pickup (42) includes an electrical contact (44) that engages a slip ring (48) associated with the rotor (32). The current measurement module also includes a first current measurement device (50) mounted relative to the electrical pickup (42) to detect at least a current flowing through the electrical pickup; and a second current measurement device (52) mounted relative to the electrical pickup (42) to detect at least a current flowing through a component associated with the gearbox output shaft.

Description

[0001] This application is a divisional application of the invention patent application with the application date of December 17, 2019, application number 201980085099.0 (international application number: PCT / DK2019 / 050403), and invention name “Improvements related to stray current detection in wind turbine generators”. Technical Field

[0002] The present invention relates to a wind turbine generator equipped with means for monitoring stray currents through various components of the generator in order to provide diagnostics and protection. Background Art

[0003] Wind turbines use a large rotor with multiple rotor blades to convert kinetic energy from the wind into electrical energy. A typical horizontal axis wind turbine (HAWT) includes a tower, a nacelle located on top of the tower, a rotating hub or "rotor" mounted to the nacelle, and multiple wind turbine rotor blades coupled to the hub. The nacelle houses many functional components of the wind turbine, including, for example, a generator, a gearbox, a drive train, and a rotor brake assembly, as well as a converter device for converting mechanical energy at the rotor into electrical energy to be provided to the power grid. The gearbox increases the speed of the low-speed main shaft and drives the gearbox output shaft. The gearbox output shaft then drives a generator that converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator can then be converted as needed before being supplied to appropriate power consumers, such as a power grid distribution system.

[0004] In wind turbine systems, generators inevitably generate high voltages, especially for modern wind turbines, which strive for high-voltage power generation for electrical efficiency. However, a challenge in designing such generator components is that the generated high voltages can also induce unintended currents in other components of the generator and associated components. These so-called "stray currents" can cause arcing between adjacent components, which in turn can lead to damage such as pitting and welding. Bearings are particularly susceptible to this damage, so it is desirable to detect these "stray currents" within acceptable levels. It is also desirable to direct these currents along a path to ground so that they do not cause problems.

[0005] It is in this context that the present invention is designed. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided a power generation assembly for a wind turbine. The power generation assembly comprises a gearbox including a gearbox output shaft; a generator including a rotor coupled to the gearbox output shaft; and a current measurement module located between the gearbox and the generator. The current measurement module comprises an electrical pickup mounted to the power generation assembly, wherein the electrical pickup comprises electrical contacts that engage slip rings associated with the rotor. The current measurement module further comprises a first current measurement device mounted relative to the electrical pickup to detect a current flowing through the first current measurement device; and a second current measurement device mounted relative to the electrical pickup to detect a current flowing through a component associated with the gearbox output shaft.

[0007] The above-described assembly is advantageous because it enables easy diagnosis of stray current levels in various components of the power generation assembly, particularly in generator components, such as the rotor. Furthermore, the above-described assembly can be configured to prevent excessive accumulation of stray currents by, for example, initiating protective measures if stray currents detected in certain components exceed predetermined thresholds. This advantageously helps prevent damage to critical turbine components that could result from arcing caused by stray currents.

[0008] Note that preferably, in use, the electric pick-up is stationary relative to the rotor in the sense that it does not rotate with the rotor.

[0009] In a preferred embodiment of the present invention, the current measurement module is provided as an integrated unit. Providing the current measurement module as an integrated unit, i.e. all components are somehow mounted together as a unit before installation, increases the ease of installing the module at the desired location between the generator and the gearbox.

[0010] In some embodiments, each of the first and second current measurement devices includes an elongated sensing element arranged to substantially surround the generator rotor. Because the current measurement devices surround the generator rotor, they can readily detect stray currents accumulated not only within at least the rotor, but also within any device electrically connected to the current measurement device, either capacitively or galvanically. Each of the first and second current measurement devices can include a Rogowski coil. Thus, the current measurement devices are configured to detect current in any component located radially inward of the aperture defined by the loop of the measurement device.

[0011] In some embodiments, the first current measuring device is mounted radially outside the electric pickup device, and the second current measuring device is mounted radially inside the electric pickup device.

[0012] The above-described arrangement of current measuring devices provides a useful mechanism for distinguishing between stray currents detected at two radial locations. In particular, this arrangement enables the determination of the stray current generated by the generator rotor (and cleared by the electrical pickup device), which will correspond to the difference between the currents detected by the two devices. This, in turn, enables stray current diagnostics and protective measures specifically for the generator.

[0013] Optionally, the current measurement module further comprises a mounting plate. The electrical contacts and the first and second current measurement devices are configured to be mounted to the mounting plate. In some embodiments, the mounting plate is configured to be mounted to a gearbox housing. Providing the current measurement module as an integrated unit in this manner, i.e., all components are mounted to the mounting plate (and preferably, the mounting plate substantially surrounds the rotor), facilitates mounting the module at a desired location between the generator and the gearbox.

[0014] In some embodiments, the power generation assembly further includes a control system in operative communication with the current measurement module, the control system being configured to identify anomalies in the detected current based on the current detected by the first current measurement device and / or the second current measurement device. The current measurement module thereby facilitates stray current diagnostics and protection measurements for various components of the power generation assembly, particularly the generator.

[0015] In some embodiments, the electrical pickup device includes a brush module. Optionally, the brush module may include one or more linear brushes. In this context, the term "linear" is used to indicate that the individual elements (e.g., filaments or fibers) forming the brush array are arranged in a generally planar manner relative to one another. In other words, the individual filament / fiber elements forming the brush array may be arranged generally parallel to one another, for example, in a row along a channel provided in the brush assembly.

[0016] In this case, the one or more linear brushes may extend along an axis that is substantially aligned with the axis of rotation of the rotor.However, in another embodiment, the dual current sensor may be combined with an electrical pick-up having brushes arranged in a radial direction relative to the rotor.

[0017] Optionally, the one or more linear brushes are carbon fiber brushes.Alternatively, other conductive materials may be used to form the individual brush elements, such as copper or brass wire or braid.

[0018] According to another aspect of the present invention, a wind turbine is provided, comprising a power generation assembly substantially as described above. Specifically, the wind turbine comprises a wind turbine tower, a nacelle rotatably coupled to the tower, a rotating hub mounted to the nacelle, and a plurality of wind turbine blades coupled to the hub. The nacelle includes the power generation assembly.

[0019] According to another aspect of the present invention, a power generation assembly for a wind turbine is provided. The power generation assembly includes a gearbox including a gearbox output shaft; a generator including a rotor coupled to the gearbox output shaft; and an electrical pickup device mounted to the power generation assembly. The electrical pickup device includes a contact disk associated with and extending radially away from the generator rotor; and at least one electrical contact aligned with the axis of the generator rotor and configured to electrically contact an electrical contact surface of the contact disk to pick up current from a component of the power generation assembly.

[0020] Providing the above-described electrical pickup configuration is particularly advantageous because it facilitates blind integration of the electrical pickup assembly into its desired location between the generator and the gearbox (the latter two components already being mounted within the nacelle prior to integration of the electrical pickup assembly). The axial orientation of the electrical contacts also increases the flexibility of the electrical pickup assembly for use with a plurality of different generators, each having a different rotor diameter. It should be understood that the above description of "alignment" with the generator rotor axis should not be strictly limited to "parallel alignment." The electrical contacts may actually be slightly angled relative to the generator rotor axis as long as the desired electrical contact with the contact disc is achieved (i.e., as long as the electrical contacts do not extend perpendicular to the generator rotor axis).

[0021] In some embodiments, the at least one electrical contact comprises a linear brush array. Optionally, the brush array comprises a plurality of brush fibers extending in a direction aligned with (and preferably substantially parallel to) the axis of rotation of the generator rotor so as to mate with the electrical contact surface of the contact disk. The axially oriented arrangement of the electrical contact brush array (in combination with the radially extending contact disk) ensures a good electrical connection between the electrical pickup device and the rotor without requiring precise, detailed alignment of the electrical contacts with the rotor (as might be required with axially oriented contacts).

[0022] In some embodiments, the electrical contacts are secured to a mount associated with the housing of the gearbox.

[0023] The electrical contact pickup device may include a first current measuring device mounted relative to the electrical pickup device to detect current flowing therethrough and / or a second current measuring device mounted relative to the electrical pickup device to detect current flowing through a component associated with the gearbox output shaft. In such an embodiment, each of the first current measuring device and the second current measuring device may include an elongated sensing element arranged to substantially surround the generator rotor.

[0024] Optionally, the first current measuring device is mounted on a radially outer side of the electric pickup device, and the second current measuring device is mounted on a radially inner side of the electric pickup device.

[0025] According to another aspect of the present invention, a wind turbine is provided, comprising a power generation assembly substantially as described above. Specifically, the wind turbine comprises a wind turbine tower, a nacelle rotatably coupled to the tower, a rotating hub mounted to the nacelle, and a plurality of wind turbine blades coupled to the hub. The nacelle includes the power generation assembly.

[0026] It is expressly intended that within the scope of this application, the various aspects, embodiments, examples and alternatives set forth in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular individual features thereof, may be employed independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination, unless such features are incompatible. Applicants reserve the right to change any initially filed claim or to file any new claim accordingly, including the right to amend any initially filed claim to subordinate and / or incorporate any feature, even though no other claim was initially claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0028] Figure 1 is a schematic diagram of a wind turbine in which a power generation assembly according to an embodiment of the present invention may be implemented;

[0029] Figure 2 is located in Figure 1 Schematic diagram of various functional power generation components within a wind turbine nacelle;

[0030] Figure 3 yes Figure 2 A cross-sectional view of the generator shown;

[0031] Figure 4 is a perspective view of a portion of a gearbox and a portion of a rotor of a generator, illustrating the implementation and location of a current measurement module according to an embodiment of the present invention;

[0032] Figure 5 yes Figure 4 A close-up view of the arrangement showing details of the construction of the current measurement module; and

[0033] Figure 6 1 is a perspective view of a current measurement module implemented on a generator rotor according to an embodiment of the present invention, viewed from different perspectives.

[0034] In the drawings, like features are indicated by like reference numerals. DETAILED DESCRIPTION

[0035] Specific embodiments of the present invention will now be described, wherein many features will be discussed in detail in order to provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details, and in some cases, well-known methods, techniques, and structures have not been described in detail to avoid unnecessarily obscuring the present invention.

[0036] To place the embodiments of the present invention in proper context, reference is first made to Figure 1 , which shows a typical horizontal axis wind turbine (HAWT) in which power generation assemblies according to embodiments of the present invention may be implemented. Although this particular image depicts an onshore wind turbine, it will be understood that equivalent features will also be found on offshore wind turbines. Furthermore, although the wind turbine is referred to as "horizontal axis," those skilled in the art will understand that for practical purposes, the axis is typically slightly tilted to prevent contact between the rotor blades and the wind turbine tower in strong winds.

[0037] As previously mentioned, wind turbine 1 includes a tower 2, a nacelle 4 rotatably coupled to the top of tower 2 by a yaw system (not shown), a rotating hub or "rotor" 8 mounted to nacelle 4, and a plurality of wind turbine rotor blades 10 coupled to hub 8. Nacelle 4 and rotor blades 10 are rotated and directed into the wind by the yaw system.

[0038] Reference Figure 2Nacelle 4 may include a power generation assembly 20 comprising a gearbox 22 and a generator 24. A main shaft 26 is supported by a main bearing housing 25 and is connected to and driven by the rotor 8, providing input drive to the gearbox 22. The gearbox 22 increases the speed of the low-speed main shaft 26 via internal gears (not shown) and drives a gearbox output shaft (not shown). The gearbox output shaft, in turn, drives a generator 24, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator 24 may then be converted by other components (not shown) as needed before being supplied to appropriate power consumers (e.g., a grid distribution system). So-called "direct drive" wind turbines that do not utilize a gearbox are also known. In direct drive wind turbines, the generator is driven directly by a shaft connected to the rotor. A so-called "pitch tube" 27 may be arranged to pass through the center of the generator 24 and gearbox 22 to provide hydraulic service to the wheel hub.

[0039] The gearbox 22 and the generator 24 may be coupled together in an integrated unit to form the power generation assembly 20. Such an integrated unit may be Figure 2 As shown in Figure 3 By way of specific example, a longitudinal section through a generator is shown, with such an integrated unit as a separate subassembly of the generator.

[0040] Referring generally to the gearbox 22, the gearbox housing 30 is generally cylindrical in form and is oriented such that its primary axis of rotation (at Figure 3 The cylindrical configuration of the gearbox housing 30 is due to the specific type of gearbox used in the illustrated embodiment, which is a planetary gearbox. As is known to those skilled in the art, a planetary gearbox comprises a series of planetary gears arranged around a central sun gear, and these planetary gears are collectively arranged within a surrounding ring gear. The ratio of the number of teeth between the ring gear, the planetary gears, and the sun gear determines the gear ratio of the gearbox. For the sake of clarity, the details of the gearbox will not be described in further detail here, as the gearbox is not the primary subject of the present invention. It can be said that other gearbox configurations may also be used, although it is presently envisioned that the planetary gearbox provides an elegant solution suitable for the range of wind turbine nacelles.

[0041] Turning now to the generator 24, the output shaft of the gearbox 22 cooperates with the rotor 32 of the generator 24, as shown in FIG. Figure 3 The generator 24 in the illustrated embodiment is an IPM (interior permanent magnet) motor having an outer stator 36 surrounding a rotor 32. The rotor 32 includes a rotor shaft 32a coupled to a gearbox output shaft (not shown), and a radially outer rotor core 32b that carries, supports, or otherwise houses the permanent magnet elements of the rotor 32.

[0042] The stator 36 includes a stator core 38 surrounding the rotor core 32 b.

[0043] Reference Figure 4 , the current measurement module 40 can be incorporated into the generator-gearbox integrated assembly and located between the gearbox and the generator. Specifically, the current measurement module 40 in the illustrated embodiment is associated with and cooperates with the generator rotor 32. At this point, it should be noted that the current measurement module 40 is also Figure 3 , and is highlighted by the circle marked "A". However, for ease of understanding, Figure 4 The current measurement module 40 is shown in more detail. Figure 5 The position and configuration of the current measurement module 40 are shown in more detail in the close-up view of FIG.

[0044] like Figures 4 to 6 As shown in varying degrees of detail in Figure 1 , the current measurement module 40 shown includes an electrical pickup 42 that is arranged to clear "stray currents" induced in components of the generator 24. The electrical pickup 42 is mounted so as to be stationary relative to the generator rotor 32 during use. In the embodiment shown, the electrical pickup 42 includes a plurality of electrical contacts 44 that are mounted to a mounting plate or bracket 46 and are arranged to surround the gearbox output shaft and the generator rotor 32. Each of the electrical contacts 44 engages and mates with a flange or slip ring 48 that is associated with the rotor 32 and extends radially away from the rotor. The electrical contacts are made of a conductive material, such as carbon fiber or copper, and may take the form of an array of brushes. These will be described in more detail below.

[0045] The current measurement module 40 also includes a first current measurement device 50 and a second current measurement device 52, which are configured to measure the current flowing through the components of the generator-gearbox integrated assembly. In the embodiment shown, the first current measurement device 50 and the second current measurement device 52 each correspond to an elongated current measurement element that substantially surrounds the axis of rotation of the generator 24. Specifically, each device 50, 52 is a Rogowski coil, which, as known to those skilled in the art, is actually a flexible current transformer that is arranged to enable monitoring and measurement of alternating current. Figure 5 As shown ( Figure 6), a pair of current-measuring Rogowski coils 50, 52 are concentrically mounted to the mounting disk 46 such that each coil 50, 52 extends in a loop between the electrical contacts 44 and substantially surrounds the gearbox output shaft and the radially inward portion of the generator rotor 32. The Rogowski coils 50, 52 are mounted to the mounting disk 46 using a fastening device 53 (e.g., a clamp) and positioned on diametrically opposite sides of the electrical contacts 44; in other words, the electrical contacts 44 are located between the two coils 50, 52. This configuration provides a particularly elegant and compact arrangement, but it is contemplated that in some embodiments, the electrical contacts 44 may be arranged in a different location.

[0046] In the illustrated embodiment, each of the Rogowski coils 50, 52 is configured to monitor and measure the current induced in a component (or components) located radially inwardly of the Rogowski coil in question, that is, the components surrounded by the coil. Specifically, the first current measuring Rogowski coil 50 is mounted at a radially outer position on the mounting disk 46 relative to the electrical contact 44 and is configured to measure the current induced in and flowing through the electrical contact 44, and therefore the current in the electrical pickup device 42 as a whole, as well as the current in other components radially inwardly of the coil 50. The second current measuring Rogowski coil 52 is mounted at a radially inner position on the mounting disk 46 relative to the electrical contact 44 and is configured to measure the current induced in and flowing through the component located radially inwardly of the electrical pickup device 42, such as the gearbox output shaft and the pitch tube 27 ( Figures 4 to 6 Not shown, but in Figure 2 ) and the generator rotor 32.

[0047] The loose ends of a pair of Rogowski coils 50, 52 extend radially outwardly away from the electrical pickup 42 to a connection or interface (at Figure 5, the circuit system is configured to monitor and analyze the output signals from the Rogowski coils 50, 52, and may also include, for example, a generator control unit or system data bus configured to take action based on the measured "stray current" value, or be in operative communication with the generator control unit or system data bus. For example, the difference in the currents measured by the pair of Rogowski coils 50, 52 will correspond to the "stray current" accumulated in the electrical contacts 44 (e.g., from the generator rotor 32 and the pitch tube 28). Thus, the illustrated embodiment enables diagnostics of, for example, the level of stray current in the generator 24 to be performed. Furthermore, protective action may also be taken if the stray current value measured by one or both of the Rogowski coils 50, 52 exceeds a predetermined threshold. As a result, the accumulation of stray current in the generator 24 can be easily detected and protective measures implemented to avoid or mitigate any arcing and associated damage that may result.

[0048] Figure 6 A close-up side perspective view is shown in FIG. 4, highlighting additional details of the construction of the current measurement module 40; this view is taken along Figure 5 The cross section is taken vertically, perpendicularly through the axis of the mounting plate 46, but also shows the left hand side of the current measurement module 40 that is not in the Figure 5 Other components in.

[0049] Figure 6 The mounting disk 46 is shown to include a plurality of supports 55 in the form of shelves or ledges, each of which extends perpendicular to the annular main surface of the mounting disk 46 and substantially parallel to the axis of rotation of the generator 24. Each shelf supports a respective one of the electrical contacts 44, which are mounted to their respective supports 55 by fastening means (not shown), such as bolts. In the illustrated embodiment, as previously described, each electrical contact 44 takes the form of a generally linear brush array comprising a plurality of brush filaments or fibers extending outwardly aligned with and preferably substantially parallel to the axis of rotation of the generator 24 (and also substantially parallel to the respective supports 55) to engage the slip ring 48 associated with the rotor 32. The term "linear" is used herein to indicate that the brush fibers are arranged in a generally planar manner, for example, along a linear channel provided in the electrical contact and positioned parallel to one another within the linear channel. However, it should be understood that precise parallel alignment of the axially extending brush fibers relative to the axis of rotation of the generator 24 is not required for electrical connectivity between the electrical contacts 44 and the slip rings 48. The brush fibers may be made of carbon fiber or any suitable conductive material such as copper or graphite.

[0050] It will be appreciated that the axially extending alignment of the brush fibers, combined with the provision of radially extending slip rings 48 associated with the rotor 32, is particularly advantageous. This is because it increases the flexibility of the illustrated electrical pickup device 42 for use with a variety of generators having different rotor shaft diameters. Furthermore, it should be noted that due to the size of the generator 24 and gearbox 22 assembly and the process by which they are installed within the wind turbine nacelle 4, the current measurement module 40 must, in effect, be incorporated into its desired location (between the gearbox 22 and the generator 24) via a "blind assembly" process. The configuration of the electrical pickup device used in embodiments of the present invention increases the ease with which blind assembly can be performed while ensuring that the brush fibers (when installed in place) will still maintain good electrical connectivity with the generator rotor 32 via the slip rings 48; however, the requirement to precisely align the brush fibers with components such as the generator rotor 32 and / or the main shaft 26 is eliminated. The advantages of the illustrated configuration are particularly evident when compared to electrical pickup devices comprising a brush array in which the brush fibers extend radially inward (e.g., as a ring around the generator's axis of rotation).

[0051] Many modifications may be made to the examples described above without departing from the scope of the invention as defined in the appended claims.

Claims

1. A power generation assembly (20) for a wind turbine (1), the power generation assembly comprising: A gearbox (22), the gearbox comprising a gearbox output shaft; a generator (24) comprising a rotor (32) coupled to the gearbox output shaft; as well as An electric pickup device (42) is mounted to the power generation assembly, the electric pickup device comprising: a contact disk (48) associated with the generator rotor (32) and extending radially away from the generator rotor; as well as At least one electrical contact (44) is parallel to the axis of the generator rotor (32) and is configured to electrically contact the electrical contact surface of the contact disk (48) to pick up electrical current from a component of the power generation assembly.

2. The power generation assembly according to claim 1, wherein: The at least one electrical contact includes a brush array.

3. The power generation assembly according to claim 2, wherein: The brush array includes a plurality of brush fibers extending in a direction parallel to a rotation axis of the generator rotor so as to cooperate with the contact disk.

4. The power generation assembly according to claim 2, wherein: The brush array is a linear brush array.

5. The power generation assembly according to any one of claims 1 to 4, wherein: The electrical contacts are secured to mounts associated with the housing of the gearbox.

6. The power generation assembly according to any one of claims 1 to 4, wherein: The electrical contact comprises a first current measuring device mounted relative to the electrical pickup to detect at least a current flowing through the electrical pickup and / or a second current measuring device mounted relative to the electrical pickup to detect at least a current flowing through a component associated with the gearbox output shaft.

7. The power generation assembly of claim 6, each of the first and second current measurement devices comprising an elongated sensing element arranged to substantially surround the generator rotor.

8. The power generation assembly according to claim 6, wherein the first current measuring device is installed on a radially outer side of the electric pickup device, and the second current measuring device is installed on a radially inner side of the electric pickup device.

9. A wind turbine comprising a power generating assembly according to any one of the preceding claims.

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