Patent Description:
Wind turbines convert kinetic energy from the wind into electrical energy, using a large rotor with a number of rotor blades. A typical Horizontal Axis Wind Turbine (HAWT) comprises a tower, a nacelle on top of the tower, a rotating hub or 'rotor' mounted to the nacelle and a plurality of wind turbine rotor blades coupled to the hub. The nacelle houses many functional components of the wind turbine, including for example a generator, gearbox, drive train and rotor brake assembly, as well as convertor equipment for converting the mechanical energy at the rotor into electrical energy for provision to the grid. The gearbox steps up the rotational speed of the low speed main shaft and drives a gearbox output shaft. The gearbox output shaft in turn drives the generator, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator may then be converted as required before being supplied to an appropriate consumer, for example an electrical grid distribution system.

In a wind turbine system, the generator necessarily generates high voltages, and this is particularly true for modern-day wind turbines which pursue high voltage generation for electrical efficiency. However, a challenge to the design of such generator assemblies is that the generated high voltages can also induce unintentional currents in other components of the generator and associated components. These so-called 'stray currents' can result in electrical arcing between adjacent components, and this can, in turn, cause damage such as pitting and welding. Bearings are particularly susceptible to this kind of damage and so it is desirable to detect that such 'stray currents' are within acceptable levels. It is also desirable to channel such currents along grounding routes that will not cause problems.

<CIT> is a relevant example of prior art in this field.

According to a first non claimed aspect of the invention, there is provided an electrical power generating assembly for a wind turbine. The electrical power generating assembly comprises a gearbox comprising a gearbox output shaft, a generator comprising a rotor that is coupled to the gearbox output shaft; and a current measuring module located between the gearbox and the generator. The current measuring module comprises: an electrical pickup mounted to the electrical power generating assembly wherein the electrical pickup includes an electrical contact that engages with a slip ring associated with the rotor. The current measuring module further comprises: a first current measuring device mounted with respect to the electrical pickup to detect current flowing therethrough; and a second current measuring device mounted with respect to the electrical pickup to detect current flowing through a component associated with the gearbox output shaft.

The above-described assembly is advantageous as it enables diagnostics of stray current levels in various components of the electrical power generating assembly (and particularly in the generator components such as the rotor) to be easily carried out. Furthermore, the above-described assembly may be configurable to prevent excess build-up of stray currents by, for example, taking protective measures if the detected stray current in certain components exceeds a predetermined threshold. This advantageously helps to prevent damage to key turbine components that may result from electrical arcing caused by the stray currents.

Note that, preferably, the electrical pickup is stationary with respect to the rotor, in use, in the sense that the electrical pickup does not rotate with the rotor.

In a preferred embodiment of the invention, the current measuring module is provided as an integrated unit. Providing the current measuring module as an integrated unit, with all of the components being mounted together somehow to one unit prior to installation increases the ease of installation of the module in its desired location between the generator and gearbox.

In some embodiments, each of the first and second current measuring devices comprises an elongate sensing element arranged to substantially encircle the generator rotor. As the current measuring devices encircle the generator rotor, they are able to easily detect stray current that builds up at least within the rotor, but also anything electrically connected to it either capacitively or galvanically. Each of the first and second current measuring devices may comprise a Rogowski coil. Thus, the current measuring devices are configured to detect current in any component located radially inward of the aperture defined by the loop of the measuring device.

In some embodiments, the first current measuring device is mounted radially-outboard of the electrical pickup, and the second current measuring device is mounted radially-inboard of the electrical pickup.

The above-described arrangement of current measuring devices provides a useful mechanism for differentiating between stray current detected at the two radial locations. In particular, this arrangement enables a determination of the stray current produced by the generator rotor (and scavenged by the electrical pickup) to be carried out - this stray current will correspond to the difference between the current detected by the two devices. This thereby enables stray current diagnostic and protection measures to be implemented specifically in respect of the generator.

Optionally, the current measuring module further comprises a mounting disk. The electrical contact, and the first and second current measuring devices are configured to be mounted to the mounting disk. In some embodiments, the mounting disk is configured to be mounted to a housing of the gearbox. Providing the current measuring module in the above-described manner as an integrated unit, with all of the components being mounted to a mounting disk (and preferably one that substantially encircles the rotor), increases the ease of installation of the module in its desired location between the generator and gearbox.

In some embodiments, the electrical power generating assembly further comprises a control system in operative communication with the current measuring module, the control system configured to identify, based on the current detected by the first and/or second current measuring device, anomalies in the detected current. The current measuring module thereby facilitates the implementation of stray current diagnostic and protection measures in respect of various components of the electrical power generating assembly, particularly the generator.

In some embodiments, the electrical pickup comprises a brush module. Optionally, the brush module may comprise one or more linear brushes. In this case, the term 'linear' is used to indicate that individual elements forming the brush array (e.g. filaments or fibres) are arranged in a generally planar manner with respect to one another. In other words, the individual filament/fibre elements forming the brush array may be arranged generally parallel to one another, for example in a line along a channel provided in the brush component.

In such cases, the one or more linear brushes may extend along an axis that is generally aligned with a rotational axis of the rotor. However, in another embodiment, the dual current sensors may be combined with an electrical pickup that has brushes arranged in a radial direction relative to the rotor.

Optionally, the one or more linear brushes are carbon fibre brushes. Alternatively, other electrically conductive materials could also be used to form the individual brush elements, such as copper or brass wires or braids.

According to another non claimed aspect of the present invention, there is provided a wind turbine comprising the electrical power generating assembly substantially as described hereinabove. In particular, 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 comprises the electrical power generating assembly.

According to another aspect of the present invention as claimed in claim <NUM>, there is provided an electrical power generating assembly for a wind turbine. The electrical power generating assembly comprises a gearbox comprising a gearbox output shaft, a generator comprising a rotor that is coupled to the gearbox output shaft; and an electrical pickup mounted to the electrical power generating assembly. The electrical pickup comprises: a contact disk associated with and extending radially away from the generator rotor; and at least one electrical contact parallel with a rotational axis of the generator rotor, and configured to be in electrical contact with an electrical contact surface of the contact disk so as to pick up current from components of the electrical power generating assembly.

Providing the above-described electrical pickup configuration is particularly advantageous as it facilitates blind integration of the electrical pickup assembly into its desired location between the generator and gearbox (the latter two components having already been installed 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 multiple different generators, each having a different rotor diameter. It will be appreciated that the above description of 'alignment' with the generator rotor axis should not be limited strictly to 'parallel alignment'. The electrical contacts may in fact be angled slightly with respect to the generator rotor axis, provided the required electrical contact with the contact disk is attained (i.e. provided the electrical contacts do not extend perpendicular to the generator rotor axis).

In some embodiments, the at least one electrical contact comprises a linear electrical brush array. Optionally, the electrical brush array comprises a plurality of brush fibres, extending in a direction aligned with (and preferably substantially parallel) to a rotational axis of the generator rotor, so as to interface 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 good electrical connection between the electrical pickup and the rotor without requiring precise detailed alignment of the electrical contacts with the rotor (as might be required for axially-oriented contacts). In some embodiments, the electrical contact is affixed to a mount associated with a housing of the gearbox.

The electrical contact pickup may comprise a first current measuring device mounted with respect to the electrical pickup to detect current flowing therethrough and/or a second current measuring device mounted with respect to the electrical pickup to detect current flowing through a component associated with the gearbox output shaft. In such embodiments, each of the first and second current measuring devices may comprise an elongate sensing element arranged to substantially encircle the generator rotor. Optionally, the first current measuring device is mounted radially-outboard of the electrical pickup, and the second current measuring device is mounted radially-inboard of the electrical pickup.

According to another aspect of the present invention as claimed in claim <NUM>, there is provided a wind turbine comprising the electrical power generating assembly substantially as described hereinabove. In particular, 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 comprises the electrical power generating assembly.

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

In the drawings, like features are denoted by like reference signs.

A specific embodiment of the invention will now be described in which numerous 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 the skilled person that the invention may be put in to effect without the specific details and that in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

In order to place the embodiments of the invention in a suitable context, reference will firstly be made to <FIG>, which illustrates a typical Horizontal Axis Wind Turbine (HAWT) in which an electrical power generating assembly according to an embodiment of the invention may be implemented. Although this particular image depicts an on-shore wind turbine, it will be understood that equivalent features will also be found on off-shore wind turbines. In addition, although the wind turbines are referred to as 'horizontal axis', it will be appreciated by the skilled person that for practical purposes, the axis is usually slightly inclined to prevent contact between the rotor blades and the wind turbine tower in the event of strong winds.

As previously mentioned, the wind turbine <NUM> comprises a tower <NUM>, a nacelle <NUM> rotatably coupled to the top of the tower <NUM> by a yaw system (not shown), a rotating hub or 'rotor' <NUM> mounted to the nacelle <NUM> and a plurality of wind turbine rotor blades <NUM> coupled to the hub <NUM>. The nacelle <NUM> and rotor blades <NUM> are turned and directed into the wind direction by the yaw system.

With reference to <FIG>, the nacelle <NUM> may include an electrical power generating assembly <NUM>, which includes a gearbox <NUM> and a generator <NUM>. A main shaft <NUM>, is supported by a main bearing housing <NUM> and is connected to, and driven by, the rotor <NUM> and provides input drive to the gearbox <NUM>. The gearbox <NUM> steps up the rotational speed of the low speed main shaft <NUM> via internal gears (not shown) and drives a gearbox output shaft (not shown). The gearbox output shaft in turn drives the generator <NUM>, which converts the rotation of the gearbox output shaft into electricity. The electricity generated by the generator <NUM> may then be converted by other components (not shown) as required before being supplied to an appropriate consumer, for example an electrical grid distribution system. So-called "direct drive" wind turbines that do not use gearboxes are also known. In a direct drive wind turbine, the generator is directly driven by a shaft connected to the rotor. A so called 'pitch tube' <NUM> may be arranged to pass along the centre of the generator <NUM> and the gearbox <NUM> to provide hydraulic services to the hub.

The gearbox <NUM> and generator <NUM> may be coupled together in an integrated unit to form the electrical power generating assembly <NUM>. Such an integrated unit is shown in <FIG>, whereas <FIG> shows a longitudinal section through the generator by way of a specific example, and as a separate sub assembly to the generator.

With reference generally to the gearbox <NUM>, a gearbox housing <NUM> is generally cylindrical in form and is oriented such that its major rotational axis (indicated by the line 'Y' in <FIG>) is horizontal, in the orientation of the drawings. The cylindrical configuration of the gearbox housing <NUM> is due to the specific type of gearbox that is used in the illustrated embodiment, which is an epicyclic gearbox. As the skilled person would know, an epicyclic gearbox comprises a series of planet gears that are arranged about a central sun gear, and which collectively are arranged within an encircling ring gear. The ratio of the number of teeth between the ring gear, the planet gear and the sun gears determines the gear ratio of the gearbox. For clarity, fine detail of the gearbox will not be described in further detail here as the gearbox is not the principal subject of the invention. Suffice to say that other gearbox configurations could also be used, although it is currently envisaged that an epicyclic gearbox provides an elegant solution fit for the confines of a wind turbine nacelle.

Turning now to the generator <NUM>, the output shaft of the gearbox <NUM> interfaces with a rotor <NUM> of the generator <NUM>, as can be seen particularly clearly in the section view of <FIG>. The generator <NUM> in the illustrated embodiment is an IPM (interior permanent magnet) electric machine having an external stator <NUM> which surrounds the rotor <NUM>. The rotor <NUM> includes a rotor shaft 32a which couples to a gearbox output shaft (not shown), and a radially out rotor core 32b which carries, support or other houses the permanent magnet elements of the rotor <NUM>.

The stator <NUM> includes a stator core <NUM> which surrounds the rotor core 32b.

With reference to <FIG>, a current measuring module <NUM> may be incorporated into the generator-gearbox integrated assembly, and is located between the gearbox and the generator. Specifically, the current measuring module <NUM> in the illustrated embodiment is associated with and interfaces with the generator rotor <NUM> It will be noted at this point that the current measuring module <NUM> is also shown in <FIG>, and is highlighted by the circles labelled 'A'. However, <FIG> shows the current measuring module <NUM> in more detail for ease of understanding. The location and configuration of the current measuring module <NUM> are shown in greater detail in the close-up illustration of <FIG>.

As may be seen in varying degrees of detail in <FIG>, the illustrated current measuring module <NUM> comprises an electrical pickup <NUM> which is arranged to scavenge 'stray current' induced in components of the generator <NUM>. The electrical pickup <NUM> is mounted so as to be stationary with respect to the generator rotor <NUM> in use. In the illustrated embodiment, the electrical pickup <NUM> comprises a plurality of electrical contacts <NUM> that are mounted to a mounting disk or bracket <NUM> and arranged to encircle the gearbox output shaft and the generator rotor <NUM>. Each of the electrical contacts <NUM> engages and interfaces with a flange or slip ring <NUM> that is associated with and extends radially away from the rotor <NUM>. The electrical contacts are made of electrically conductive material (for example, carbon fibre or copper) and may take the form of electrical brush arrays. These are described in greater detail below.

The current measuring module <NUM> further comprises first and second current measuring devices <NUM>, <NUM> which are configured to measure current flowing through components of the generator-gearbox integrated assembly. In the illustrated embodiment, the first and second current measuring devices <NUM>, <NUM> each correspond to an elongate current-measuring element that substantially encircles the rotational axis of the generator <NUM>. Specifically, each device <NUM>, <NUM> is a Rogowski coil which, as the skilled person would be aware, is effectively a flexible current transformer that is arranged to enable monitoring and measurement of alternating current. As shown in <FIG> (and in greater detail in Figure <NUM>), the pair of current measuring Rogowski coils <NUM>, <NUM> are mounted concentrically to the mounting disk <NUM>, such that each coil <NUM>, <NUM> extends in a loop between the electrical contacts <NUM> and substantially encircles the gearbox output shaft, and the radially inwards parts of the generator rotor <NUM>. The Rogowski coils <NUM>, <NUM> are mounted to the mounting disk <NUM> using fastening means <NUM> (such as clamps), and are positioned on radially opposing sides of the electrical contacts <NUM>; in other words, the electrical contacts <NUM> are located in between the two coils <NUM>, <NUM>. This configuration provides a particular elegant and compact arrangement, but it is envisaged that the electrical contacts <NUM> could be arranged in a different location in some embodiments.

In the illustrated embodiment, each of the Rogowski coils <NUM>, <NUM> is configured to monitor and measure the current induced in the component (or components) located radially-inboard of the Rogowski coil in question, that is to say the components that are encircled by the coils. Specifically, the first current measuring Rogowski coil <NUM> is mounted at a radially-outboard location on the mounting disk <NUM>, relative to the electrical contacts <NUM>, and is configured to measure the current induced in and flowing through the electrical contacts <NUM>, and hence in electrical pickup <NUM> as a whole, in addition to the other components that are radially inwards of the coil <NUM>. The second current measuring Rogowski coil <NUM> is mounted at a radially-inboard location on the mounting disk <NUM>, relative to the electrical contacts <NUM>, and is configured to measure the current induced in and flowing through components located radially-inboard of the electrical pickup <NUM>, for example the gearbox output shaft and pitch tube <NUM> (not shown in <FIG>, but shown in <FIG>), as well as the generator rotor <NUM>.

Loose ends of the pair of Rogowski coils <NUM>, <NUM> extend radially outwards away from the electrical pickup <NUM> to a connection or interface (indicated in <FIG> using arrows) with electronic conversion and control circuitry <NUM>. This circuitry is configured to monitor and analyse the output signal from the Rogowski coils <NUM>, <NUM> and may also comprise or be in operative communication with, for example, a generator control unit or system data bus that is configured to take action based on the measured 'stray current' values. For example, the difference in the currents measured by the pair of Rogowski coils <NUM>, <NUM> will correspond to the 'stray current' accumulated in the electrical contacts <NUM> (e.g. from the generator rotor <NUM> and the pitch tube <NUM>). The illustrated embodiment therefore enables diagnostics of the stray current levels in, for example, the generator <NUM>, to be carried out. Furthermore, protective action may also be taken if the stray current value measured by one or both of the Rogowski coils <NUM>, <NUM> exceeds a predetermined threshold. As a result, build-up of stray current in the generator <NUM> may be easily detected and protective measures implemented, thereby avoiding or mitigating any electrical arcing and associated damage that could result.

A close-up side perspective view highlighting additional details of the current measuring module <NUM> configuration is shown in <FIG>; this view is taken vertically along a section of <FIG>, perpendicularly through the axis of the mounting disk <NUM>, but also shows further components to the left hand side of the current measuring module <NUM> that are not in <FIG>.

<FIG> shows that the mounting disk <NUM> comprises a plurality of supports <NUM> in the form of shelves or ledges, each of which extends perpendicular to the annular main face of the mounting disk <NUM>, and substantially parallel to the rotational axis of the generator <NUM>. Each shelf <NUM> supports a corresponding one of the electrical contacts <NUM>, the electrical contacts <NUM> being mounted to their respective support <NUM> by fastening means (not shown) such as bolts. In the illustrated embodiment, as previously mentioned, each electrical contact <NUM> takes the form of a generally linear electrical brush array comprising a plurality of brush filaments or fibres <NUM> which extend outwards, being aligned with and preferably substantially parallel to the rotational axis of the generator <NUM> (and also to the corresponding support <NUM>), to interface with the slip ring <NUM> that is associated with the rotor <NUM>. The term 'linear' is used here to indicate that the brush fibres <NUM> are arranged in a generally planar manner - for example, located parallel to one another along and within a linear channel provided in the electrical contact. It will be appreciated however that precise parallel alignment of the axially-extending brush fibres with respect to the rotational axis of the generator <NUM> is not required for the electrical connectivity between electrical contacts <NUM> and slip ring <NUM> to occur. The brush fibres <NUM> may be made of carbon fibre, or any suitable electrically conductive material such as copper or graphite.

It will be appreciated that the axially-extending alignment of the brush fibres <NUM>, in combination with the provision of the radially-extending slip ring <NUM> associated with the rotor <NUM>, is particularly advantageous. This is because it increases the flexibility of the illustrated electrical pickup <NUM> for use with a variety of generators having different rotor shaft diameters. In addition, it is noted that due to the size of the generator <NUM> and gearbox <NUM> assemblies, and the process of their installation within the wind turbine nacelle <NUM>, the current measuring module <NUM> effectively needs to be incorporated into its desired location (between the gearbox <NUM> and the generator <NUM>) via a 'blind assembly' process. The configuration of the electrical pickup utilised in embodiments of the invention increases the ease with which blind assembly may take place, whilst simultaneously ensuring that the brush fibres <NUM> (when installed in situ) will still have a good electrical connectivity with the generator rotor <NUM> via the slip ring <NUM>; however the requirement to have a precise alignment of the brush fibres <NUM> with components such as the generator rotor <NUM> and/or main shaft <NUM> is obviated. The advantages of the illustrated configuration are particularly evident when considered in comparison with electrical pickups comprising a brush array in which the brush fibres extend radially inwards (e.g. as a ring around the rotational axis of the generator).

Claim 1:
An electrical power generating assembly (<NUM>) for a wind turbine (<NUM>) comprising:
a gearbox (<NUM>) comprising a gearbox output shaft,
a generator (<NUM>) comprising a rotor (<NUM>) that is coupled to the gearbox output shaft; and
an electrical pickup (<NUM>) mounted to the electrical power generating assembly, characterized in that the electrical
pickup comprises:
a contact disk (<NUM>) associated with and extending radially away from the generator rotor (<NUM>); and
at least one electrical contact (<NUM>) parallel with the rotational axis of the generator rotor (<NUM>) and configured to be in electrical contact with an electrical contact surface of the contact disk (<NUM>) so as to pick up current from components of the electrical power generating assembly.