Methods for servicing active stator parts

Abstract

The present disclosure relates to methods for servicing, e.g. removing and mounting, active stator parts. A method comprises mechanically connecting a rotor and a stator of an electrical machine to obtain a rotor-stator assembly, mechanically disconnecting the stator from a supporting structure such that the rotor-stator assembly is rotatable, rotating the rotor-stator assembly such that the stator part is accessible, and servicing the active stator part.

Description

GENERAL ELECTRIC RE OVABLES ESPANA S.L. MARCH 21, 2025 701204-WO-1 P5590PC00METHODS FOR SERVICING ACTIVE STATOR PARTSTECHNICAL FIELD

[0001] The present disclosure relates to maintenance of large electrical machines, and more particularly relates to servicing, e.g. removing and installing, active stator parts of a large electrical machine. In specific examples, the present disclosure relates to removing and installing active stator parts of an electric generator of a direct drive wind turbine.BACKGROUND

[0002] Electrical machines, such as motors and generators, generally comprise a rotor structure and a stator structure. Large electrical generators may be e.g. permanent magnet excited generators (PMG). The rotor of an electrical machine rotates with respect to the stator. The rotor may be the inner structure and the stator the outer structure. The stator in this case thus surrounds, e.g. radially, the rotor. Alternatively, the configuration may be the opposite, i.e. the rotor surrounds, e.g. radially, the stator.

[0003] Such generators may be used for example in wind turbines. Wind turbines generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft either directly drives the generator rotor ("directly driven") or through the use of a gearbox.

[0004] A direct drive wind turbine generator may have e.g. a diameter of 6 - 10 meters (236 -328 inches), a length of e.g. 2 - 3 meters (79 - 118 inches) and may rotate at low speed, for example in the range of 2 to 20 rpm (revolutions per minute). Alternatively, permanent magnet generators may also be coupled to a gearbox which increases the rotational speed of the generator to, for example, between 50 to 500 rpm or even more.

[0005] In the case of permanent magnet excited generators, permanent magnets are generally comprised in the rotor (although they could also be arranged alternatively in the stator structure), whereas winding elements (e.g. coils) are usually included in the stator (although they could alternatively be arranged in the rotor structure). Permanent magnet generators are generally deemed to be reliable and require less maintenance than other generator typologies. This is animportant reason why permanent magnet generator are employed in offshore wind turbines, and particularly in direct drive offshore wind turbines.

[0006] Multiple permanent magnets may be provided in a permanent magnet module, which may be attached to the rotor as a single item. A permanent magnet module may be defined as a unit having a plurality of permanent magnets, such that the plurality of magnets can be mounted and unmounted together. Such a module may have a module base with a shape suitable for housing or carrying a plurality of permanent magnets that may be fixed to the base. The base may be configured to be fixed to a rotor structure such as a rotor rim in such a way that the plurality of magnets is fixed together to the rotor rim through the module base. The use of permanent magnet modules may facilitate the manufacturing of a rotor.

[0007] Similarly, stator coils may be grouped together in coil modules. Coil modules may be fixed to a generator structure such as a stator rim.

[0008] In large electrical machines, such as permanent magnet generators of direct drive wind turbines, it may be difficult to access a damaged coil in the stator. For example, if the coil to be replaced is close to the wind turbine tower or to a front (upwind) side of the nacelle, the damaged coil could hit the tower or the nacelle when taking it out. Likewise, if a replacement coil is to be arranged in a stator gap which is difficult to access, installing the coil may require a considerable amount of time and effort. Replacement of one or more stator coils may take several days, and even several weeks.

[0009] An easier way to replace a damaged coil in the stator could be, from a suitable position, taking out a number of coils until the damaged coil is reached. Then, from that suitable position, a new coil could be installed and the previously removed working coils could be mounted again. Installing and removing coils from a suitable position may comprise inserting and extracting the coils from a top or an upper (radial) portion of the generator. However, this may still need a significant amount of time, for example weeks.SUMMARY

[0010] According to an aspect of the disclosure, a method for servicing an active stator part of an electrical machine is provided. The method comprises mechanically connecting a rotor of the electrical machine and a stator of the electrical machine to obtain a rotor-stator assembly. The method further comprises mechanically disconnecting the stator from a supporting structure such that the rotor-stator assembly is rotatable. The method further comprises rotating the rotor-stator assembly such that the active stator part is accessible. And the method further comprises servicing the active stator part.

[0011] According to this aspect, a rotor and a stator of an electrical machine are mechanically connected in order to perform maintenance and provide access to parts of the stator that are difficult to reach. The stator is further mechanically disconnected from a structure which supports the stator. The rotor and the stator of the electrical machine can therefore rotate together. The rotor and the stator are rotated together to a position where an active stator part of the stator can be serviced.

[0012] The active stator part may therefore be serviced in a relatively easy and fast way. Operators accessing a part of the stator that is difficult to reach, e.g. in positions which would require them to work from underneath an electrical machine, may be avoided. Safety for the operators may be increased since they may remain in a place that is comfortable to access and can service the active stator part from there. Also, removing active stator parts until reaching the actual active stator part to be serviced may be avoided too. This may cause the method to be more efficient, since mechanically connecting the stator and the rotor, and then rotating the formed rotor-stator assembly, may be faster than removing working active stator parts.

[0013] In this aspect, the electrical machine may be a generator, in particular a generator of a direct drive wind turbine.

[0014] According to a further aspect of the disclosure, a method for removing an active stator part of a generator of a direct drive wind turbine is provided. The method comprises mechanically connecting a rotor of the generator and a stator of the generator to obtain a rotor-stator assembly. The method further comprises mechanically disconnecting the stator from a stator supporting structure such that the rotor-stator assembly is rotatable. The method further comprises rotating the rotor-stator assembly such that the active stator part is accessible. And the method further comprises removing the active stator part from the stator.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Non-limiting examples of the present disclosure will be described in the following, with reference to the drawings, in which:Figure 1 schematically illustrates a perspective view of one example of a wind turbine;Figure 2 illustrates an example of a hub and a nacelle of a wind turbine;Figure 3 schematically illustrates a rearview of an example of an enlarged portion of an electrical machine, specifically a generator of a direct drive wind turbine;Figure 4 shows a flowchart of an example of a method for servicing an active part of a stator of an electrical machine;Figure 5 schematically illustrates an example of a rear view of a generator of a direct drive wind turbine with four connection tools arranged in the rotor of the generator;Figure 6 schematically illustrates an example of a rear view of a generator of a direct drive wind turbine after rotating the rotor-stator assembly of figure 5;Figures 7A and 7B schematically illustrate an enlarged cross-sectional view of an electric generator of a direct drive wind turbine in which several possible locations for connection tools are indicated and in which an active part of the rotor has been replaced by a connection tool, respectively;Figure 8 schematically illustrates an enlarged rear view of a stator of a direct drive wind turbine where an active part of the rotor has been replaced by a connection tool;Figure 9 shows a flowchart of an example of a method for removing an active part of a stator of a generator of a direct drive wind turbine.DETAILED DESCRIPTION

[0016] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided byway of explanation, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the teaching. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0017] Figure 1 is a perspective view of an example of a wind turbine 10. In the example, the wind turbine 10 is a horizontal-axis wind turbine. Alternatively, the wind turbine 10 may be a vertical-axis wind turbine. In the example, the wind turbine 10 includes a tower 15 that extends from a support system 14 on a ground 2, a nacelle 16 mounted on tower 15, and a rotor 18 that is coupled to nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from the hub 20. In the example, the rotor 18 has three rotor blades 22. In an alternative embodiment, the rotor 18 includes more or less than three rotor blades 22. The tower 15 may be fabricated from tubular steel to define a cavity (not shown in figure 1) between a support system 14 and the nacelle 16. In an alternative embodiment, the tower 15 is any suitable type of a tower having any suitable height. According to an alternative, the tower can be a hybrid tower comprising a portion made of concrete and a tubular steel portion. Also, the tower can be a partial or full lattice tower.

[0018] The rotor blades 22 are spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. The rotor blades 22 are mated to the hub 20 by coupling a blade root portion 24 to the hub 20 at a plurality of load transfer regions 26. The load transfer regions 26 may have a hub load transfer region and a blade load transfer region (both not shown in figure 1). Loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26.

[0019] In examples, the rotor blades 22 may have a length ranging from about 15 meters (m) to about 90 m or more. Rotor blades 22 may have any suitable length that enables the wind turbine 10 to function as described herein. As wind strikes the rotor blades 22 from a wind direction 28, the rotor 18 is rotated about a rotor axis 30. As the rotor blades 22 are rotated and subjected to centrifugal forces, the rotor blades 22 are also subjected to various forces and moments. As such, the rotor blades 22 may deflect and / or rotate from a neutral, or non-deflected, position to a deflected position.

[0020] Moreover, a pitch angle of the rotor blades 22, i.e., an angle that determines an orientation of the rotor blades 22 with respect to the wind direction, may be changed by a pitch system to control the load and power generated by the wind turbine 10 by adjusting an angular position of at least one rotor blade 22 relative to wind vectors. Pitch axes 34 of rotor blades 22 are shown. During operation of the wind turbine 10, the pitch system may particularly change a pitch angle of the rotor blades 22 such that the angle of attack of (portions of) the rotor blades are reduced, which facilitates reducing a rotational speed and / or facilitates a stall of the rotor 18.

[0021] In the example, a blade pitch of each rotor blade 22 is controlled individually by a wind turbine controller 36 or by a pitch control system. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by said control systems.

[0022] Further, in the example, as the wind direction 28 changes, a nacelle 16 may be rotated about a yaw axis 38 to position the rotor with respect to wind direction 28.

[0023] In the example, the wind turbine controller 36 is shown as being centralized within the nacelle 16, however, the wind turbine controller 36 may be a distributed system throughout the wind turbine 10, on the support system 14, within a wind farm, and / or at a remote-control center. The wind turbine controller 36 includes a processor 40 configured to perform the methods and / or steps described herein. Further, many of the other components described herein include a processor.

[0024] As used herein, the term “processor” is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific, integrated circuit, and otherprogrammable circuits, and these terms are used interchangeably herein. It should be understood that a processor and / or a control system can also include memory, input channels, and / or output channels.

[0025] Figure 2 illustrates a simplified, internal cross-sectional view of the nacelle 16 and the rotor hub 20 of a direct drive wind turbine 10. The direct drive wind turbine may be an offshore wind turbine. As shown, the generator 3 may be coupled to the rotor hub 20 of the wind turbine 10 for generating electrical power from the rotational energy generated. Thus, rotation of the rotor hub 20 directly drives the generator 3. Other wind turbine configuration using a gearbox in between the wind turbine rotor and the generator are also known.

[0026] It should be appreciated that frame 1 and generator 3 may generally be supported by a support frame or bedplate 17 positioned atop the wind turbine tower 15. The bedplate 17 may be a bottom portion of frame 1 or may be joined to a bottom flange of a frame 1. The bedplate 17 may be rotatably mounted on the wind turbine tower 15 to rotate the nacelle about the yaw axis 38 (illustrated in figure 1).

[0027] The direct drive wind turbine 10 of figure 2 comprises a generator 3 mounted on the frame 1. The generator 3 comprises a generator stator 33 and a generator rotor 31 configured to rotate about a rotation axis 30. The frame 1 in this example comprises a rear frame or rear frame portion 19 and a front frame or forwardly protruding frame 13. The front frame 13 may be integrally formed with the rear frame 19 or may be separately formed from the rear frame. If separately formed, fasteners 4 such as bolts may join the front frame 13 to the rear frame. The front frame 13 in this example extends forward beyond the generator 3. The rear frame connects the front frame 13 to the tower 15.

[0028] A rear portion of the frame 19 may be called main frame. A main frame may transfer the loads and the vibrations acting on the rotor 18 of a wind turbine 10 to the tower 15 of the wind turbine 10, see figure 1. A main frame may be made of cast steel. A main frame may have a bottom opening, a front opening and a rear opening. The bottom opening may enable passage between the main frame and an inside of the tower 15, the front opening may enable passage between the main frame and an inside 21 of the rotor hub 20, e.g. through the front frame 13, and the rear opening may enable passage between the main frame and an inside of the nacelle 16. The front frame 13 in this example is attached to and carries the generator stator 33. The front frame 13 further supports a rotatable shaft 52.

[0029] In figure 2, the front frame 13 is an inner structure and the rotatable shaft 52 is an outer structure. In another example, the front frame 13 may be an outer structure and the rotating shaft 52 may be an inner structure. In both such examples the inner and the outer structure may rotaterelative to each other and about the rotation axis 30. For example, the shaft 52 may rotate around the front frame 13.

[0030] In the example of figure 2, the rotatable shaft 52 is rotatably supported on the front frame 13 through a front bearing 55 and a rear bearing 56. Both front and rear bearings may have rolling elements, such as balls or rollers. In some examples, the bearings may include a double tapered roller bearing. In other examples, the bearings may be journal bearings.

[0031] The rotating shaft 52 may be operatively connected to the rotor hub 20 through the generator rotor 31. The latter may be achieved, for instance, through a series of bolts 32. The bolts 32 may join the rotor hub 20, the rotatable shaft 52 and the generator rotor 31 together in such a way that at least a part of the generator rotor 31 is sandwiched by the rotor hub 20 and the rotatable shaft 52. The joint of this example is configured to transmit the rotating movement of the rotor hub 20 to the rotatable shaft 52 through the generator rotor 31. In another example, the joint may be achieved through any suitable fasteners available or even through welding.

[0032] Figure 3 schematically illustrates a rear view of an example of an enlarged portion of an electrical machine, specifically a generator 3 of a direct drive wind turbine. The illustrated back side of the generator may face a downwind side of the wind turbine (instead of the rotor of the wind turbine). In this example, the generator comprises an annular cover in its back side and comprises a plurality of segments 45, one of which has been removed in figure 3.

[0033] The generator 3 comprises a rotor 31 , a stator 33 and a radial air gap 44 between the rotor 31 and the stator 33. In the illustrated example, the rotor radially surrounds the stator. In other examples, the stator may radially surround the rotor.

[0034] The stator 33 comprises a stator rim 46 and a plurality of active stator parts 42. The rotor 31 comprises a rotor rim 47 and a plurality of active rotor parts 37. An active stator part 42 may be one or more permanent magnets, one or more permanent magnet modules, one or more coils, or one or more coil modules. An active stator part 42 may also be or comprise a pole or pole shoe. An active rotor part 37 may likewise be one or more permanent magnets, one or more permanent magnet modules or one or more coils, or one or more coil modules. For example, an active stator part 42 may be a coil, and an active rotor part 37 may be a permanent magnet module. In other examples, both the active stator parts and the active rotor parts may be coils. The radial air gap 44 is between the active parts of the rotor and the active parts of the stator.

[0035] According to an aspect of the disclosure, a method for servicing an active stator part 42 of an electrical machine 3 is provided. An example of the method is provided in the flowchart of figure 4. The method 100 comprises, at block 101 , mechanically connecting a rotor 31 and a stator 33 of the electrical machine to obtain a rotor-stator assembly. The method further comprises, at block 102, mechanically disconnecting the stator 33 from a supporting structure 1 such that therotor-stator assembly is rotatable. The disconnection of the stator 33 from the corresponding supporting structure, e.g. frame 1 or front frame 13, may in particular be performed after connecting the rotor 31 and the stator 33, forming the rotor-stator assembly. The method further comprises, at block 103, rotating the rotor-stator assembly such that the active stator part 42 is accessible. The method further comprises, at block 104, servicing the active stator part 42.

[0036] Servicing may include cleaning, inspection of parts, or in some cases may include removing the active stator part 42 from the stator 33 and e.g. complete substitution with a new active stator part.

[0037] The rotor 31 and the stator 33 may therefore be connected such that they are rotatable together. The rotor-stator assembly is therefore rotated to position the active stator part to be removed at a location that is more suitable for an operator to access, e.g. more easily and safely accessible by the operator.

[0038] The method may further comprise disconnecting, and optionally removing, elements interfering with rotation of the stator 33 and / or elements connected to the stator 33 before rotating the rotor-stator assembly. Some elements such as cables, wires, sensors, ventilation tubes and others may be connected to the stator 33 or may interfere with the stator when the stator is rotated. Therefore, these elements may be identified and removed or disconnected before the rotor-stator assembly is rotated. These elements may be removed or disconnected before mechanically connecting the rotor 31 and the stator 33 in some examples. If the electrical machine is a wind turbine generator, these elements may be stored in the nacelle 16, inside the frame 1 or in a similar suitable place until they are to be mounted again, for example once the damaged active stator part is replaced by a new active stator part.

[0039] The method may further comprise introducing one or more connection tools 35 between the rotor 31 and the stator 33 before connecting the rotor 31 and the stator 33. In the schematic examples of figures 5 and 6, four connection tools 35 are used. The one or more connection tools 35 may have a wedge shape. Wedge-shaped connection tools 35 may be easily inserted in the air gap 44 between the rotor 31 and the stator 33, see further below. The connection tools 35 may be inserted along an axial direction of the electrical machine. In other examples, the connection tools 35 do not taper or have a wedge-shape, and e.g. a height (along a radial direction of the electrical machine) of the connection tools 35 does not vary along their length. In other examples (commented on later), the connection tools 35 may be located outside the region of the air gap 44.

[0040] The method may further comprise locking the rotor 31 after introducing the one or more connection tools 35 and before connecting the rotor 31 and the stator 33. In the example of figure 5, as well as in other examples, the connection tools 35 may be first introduced between the rotor31 and the stator 33. A first connection tool 35 may be suitably arranged in and attached to the electrical machine, e.g. to the rotor 31. A second connection tool 35 may then be arranged at a suitable location. The rotor 31 may be rotated such that the operator(s) have easy access to insert the second connection tool 35. For example, if the operators are in the nacelle 16 of a direct drive wind turbine 10, the rotor 31 may be rotated until the region where the second connection tool 35 is to be inserted is in front of the operators in the nacelle 16. The same steps may be performed to install additional connection tools 35. The rotor 31 may also be rotated such that the operators can suitably install the first connection tool.

[0041] In some examples, a first connection tool and a second connection tool of the one or more connection tools are introduced at diametrically opposite locations of the electrical machine 3. These two tools, as well as other additional tools, may in general be circumferentially distributed along the electrical machine, and specifically homogeneously distributed along the circumferential direction. Homogeneously arranging the connection tools 35 along the circumferential direction of the stator 33 (and the rotor 31) may help to better distribute the loads and to effectively support the stator 33. The connection tools 35 do not all have to be the same or used exactly in the same way, to enable a force free separation of the stator 33 and supporting structure 43.

[0042] In some examples, a first connection tool and a second connection tool of the one or more connection tools are introduced in an upper half of the electrical machine 3. Arranging several connection tools 35 in the upper half of the electrical machine 3 may facilitate connecting them to the stator 33. For example, the operators may have a relatively easy access to them in order to attach them to the stator 33 if the operators are in a wind turbine nacelle 16. The upper half of the electrical machine may be understood as the half of the electrical machine which lies above the rotating axis of the electrical machine. The lower half of the electrical machine may be understood as the half of the electrical machine which lies below the rotating axis of the electrical machine.

[0043] Depending on where the connection tools 35 are to be arranged, the method may further comprise creating one or more spaces by removing one or more active rotor parts 37 of the rotor 31, and then introducing the connection tools 35 in the spaces. Depending on the structure and the specifics of the rotor 31 and stator 33 of the electrical machine, the connection tools 35 may be arranged at different locations. In some examples, the connection tools 35 may be arranged between an upwind side of the rotor 31 and an upwind of the stator 33. In the example of figure 7A, dashed region A indicates a possible location for the connection tools 35 at the upwind side of the wind turbine generator 3.

[0044] In other examples, the connection tools 35 may be arranged between a downwind side of the rotor 31 and a downwind side of the stator 33. In the example of figure 7A, dashed regionB indicates a possible location for the connection tools 35 in the back side of the generator 3. Still in other examples, the connection tools 35 may be arranged in the air gap between the rotor 31 and the stator 33. This region is indicated by dashed region C in figure 7A. The example of figure 7B shows that at least one active part 37 of the rotor 31 (shown in figure 7 A), e.g. a magnet or a magnet module, has been removed and that a connection tool 35 has been arranged in the space left by the removal of the active rotor part 37. A combination of tools in each of the regions A, B, C or any other suitable region is possible as well.

[0045] If a connection tool 35 is to be arranged in the air gap between the rotor 31 and the stator 33, e.g. radially between the rotor 31 and the stator 33, creating a space may comprise removing one or more active parts 37 of the rotor 31 , and optionally further removing one or more active parts of the stator 33. The connection tool 35 may be attached to two adjacent stator poles, for example. This option is schematically shown in the example of figure 8. In this figure, the stator poles 39 and the active parts of the stator 42, e.g. coils, are schematically illustrated. The active parts 37 of the rotor 31 may e.g. be magnets or magnet modules.

[0046] The locations at which the connection tools 35 are arranged can be combined. For example, connection tools 35 may be arranged at an upwind side and at a downwind side of the electrical machine. Or connection tools 35 may be arranged radially between the rotor 31 and the stator 33, and also at a downwind side of the electrical machine.

[0047] Once all the connection tools 35 have been arranged, they may be connected, e.g. attached, to the stator 33. To securely do this, the rotor 31 may be locked, e.g. with locking pins. In some examples, one or more locking pins may be inserted into the holes of a locking disc which is operatively connected to the rotor. The pin(s) may be arranged on the stator. The locking disc may include a plurality of holes, e.g. three or six. At predetermined positions of the rotor, the pins can be inserted in the holes on the locking disc to lock the rotor.

[0048] In some examples, the operators may move close to the connection tools 35 and manually connect them to the stator 33 (note that herein: connecting the connection tools comprises placing them in position and activating them). In other examples, connection between the connection tools 35 and the stator 33 may be remotely activated. For example, the connection tools 35 may comprise one or more engaging portions which can be caused to extend and engage the stator 33 from a remote location. Still in other examples, a manual and an automatic / remote connection between the connection tools 35 and the stator 33 may be implemented. For example, connection tools 35 which are in the upper half of the electrical machine 3 may be manually connected to the stator 33, whereas connection tools 35 which are in lower half of the generator 3 may be automatically and remotely connected to the stator 33.

[0049] Once the one or more connection tools 35 have been arranged and mechanically connect the rotor 31 and the stator 33, the rotor-assembly can be rotated together. The hatching of figures 7A and 7B show that, before the rotor-assembly is formed, the rotor is able to rotate whereas the stator is not able to rotate. And after the rotor assembly is formed due to the connection tool 35 attaching the stator 33 to the rotor 31 , the stator 33 is able to rotate with the rotor 31 (note the difference in the hatching used for the stator 33 in figures 7A and 7B). To fully enable rotation, the stator 33 is mechanically disconnected from the corresponding supporting structure(s) 43, for example a plurality of arms.

[0050] The rotor-stator assembly is then rotated to position the active stator part to be serviced 42 near, e.g. in front of, the position of the operators who may be in the nacelle. The rotor-stator assembly may for example rotate from a removal starting position to a removal end position. The starting position may e.g. include the active stator part to be removed being in the lower half of the electrical machine 3, e.g. close to a 6 o'clock position. The end position may include the active stator part to be removed being in the upper half of the generator 3, e.g. close to a 12 o'clock position.

[0051] Figure 6 schematically shows that the rotor-stator assembly has been rotated, and the active stator part to be serviced 42, e.g. a coil, was moved from being near a 6 o'clock position to being at a 12 o'clock position. If more than one active stator part is to be serviced, the rotor-stator assembly may be rotated until all of the active stator parts are serviced. The removal end position for a first active stator part may become the removal starting position for a second active stator part to be removed, and so on. In some examples, a first active stator part 42 may be removed, a new active stator part 42 may be inserted in the hole left, and then the rotor-stator assembly may be rotated to remove a second active stator part, etc.

[0052] A stator 33 of a large electrical machine, e.g. of a generator of a direct drive wind turbine 10, may weigh over 100 tons, e.g. over 150 tons. Therefore, although the rotor 31 may effectively support the stator 33 when the stator 33 is attached to the rotor 31 , gravity may cause the stator 33 to move slightly downwards. This may pose a challenge later on, when the stator 33 is to be aligned and attached to its support(s) 43 such that the rotor 31 is rotatable on its own again. Alignment may fail due to the gravity acting on the stator 33 separated from its supporting structure(s) 43. To avoid or at least mitigate this, the one or more connection tools 35 may also be compensation tools configured to compensate for gravity action on the stator 33 when mechanically disconnecting the stator 33 from the structure 43 supporting the stator.

[0053] l.e., the connection tools 35 may be configured to compensate for the effect of the gravity on the stator 33. For example, the one or more connection tools 35 may be pre-tensioned to compensate for gravity action on the stator when mechanically disconnecting the stator fromthe supporting structure , in particular such that stator forces acting on the supporting structure are removed or compensated. In other words, the connection tools 35 may exert a force on the stator 33 when attached to the stator 33. The tension or force exerted by the connection tools 35 may be such that when the stator 33 is attached to the rotor 31 and released from the supporting structure(s) 43, the stator 33 remains at a same position, specifically at a same height and tilting angle. Therefore, due to the tension of the connection tools 35, the stator 33 may be aligned with, and connected to, its supporting structure(s) 43 easily later on.

[0054] In some examples, the one or more connection tools 35 may be pre-tensioned to a predetermined tension level. The exerted force / tension level may be determined and implemented beforehand, e.g. with the help of simulations. In other examples, the tensioning may be performed in situ. The connection tools may be tensed until it is determined that the stator is no longer exerting a force on the supporting structures.

[0055] Different connection tools of the one or more connection tools may be tensioned to different tension levels. For example, a first connection tool, e.g. a tool arranged about the 12 o 'clock position before the rotor-stator assembly is rotated, may be configured to pull the stator 33. And a second connection tool, e.g. a tool arranged about the 6 o'clock position before the rotorstator assembly is rotated, may be configured to push the stator 33. The forces exerted by each connection tool 35 may be adapted to their expected circumferential positions in the electrical machine 3 when the stator 33 is released from its supporting structure(s) 43.

[0056] The electrical machine may for example be a generator, and more in particular a generator of a direct drive wind turbine 10.

[0057] The rotor-stator assembly may be rotated by wind action on one or more blades 22 of the direct drive wind turbine 10 in these examples. In other words, prevailing wind may act on the blades 22 to turn the wind turbine rotor 18, and with it, the rotor-stator assembly. The method may further comprise pitching one or more blades 22 of the direct drive wind turbine 10 to control the rotation of the rotor-stator assembly, for example the speed at which the rotor-stator assembly rotates or where the rotor-stator assembly will be stopped. Pitching may help the active stator part to be removed to end at a location easily accessible for one or more operators.

[0058] One or more brakes of the wind turbine, in particular the brake(s) to brake the generator rotor 31 , may also be used to control the rotation of the rotor-stator assembly. The calipers 11 may clamp a brake disc to brake the rotor. The calipers 11 may be attached to the rotatable shaft 52, and the brake disc brake may be attached to the front frame 13. Alternatively, the calipers 11 may be attached to the front frame 13 and the brake disc may be attached to the rotatable shaft 52. The generator rotor 31 may be braked with other types of brakes known in the art in other examples. Also the location of the brakes may be different than in the example of figure 2. In someexamples, the brake(s) may be used in addition to pitching to control the rotation of the rotor-stator assembly in a more precise manner.

[0059] The generator rotor 31 may comprise at least one encoder to monitor the rotational speed and the position (angular position) of the generator rotor 31. The data obtained by the monitoring may be used to control when, for how long and how much is braked, either by mechanically braking, i.e. applying the calipers 11, and / or by aerodynamically braking, i.e. pitching. When the rotor-stator assembly is at a desired position, e.g. a servicing position, the assembly may be kept at this position by locking the generator rotor 31. Locking pins may be used to lock the generator rotor 31 , and therefore the rotor-stator assembly, in place.

[0060] When an active stator part 42 has been moved to another circumferential position of the electrical machine 3 such that it is more easily serviceable, the operators may service it, e.g. remove it. Removal may be performed in an axial direction of the electrical machine 3 in some examples. Then, steps for the installation of a new active stator part may be performed. These steps may be in reverse order with respect to the steps of the current method. Therefore, method 100 may be a removal method and then an installation method, see further below, may be provided. Specifically, the installation method may be performed after the removal method.

[0061] Once the active stator part has been serviced, and in particular removed from the stator, a new active stator part or the same active stator part, but refurbished, may be arranged in the stator. The method may therefore comprises arranging an active stator part 42 in an opening of the stator 33 of the rotor-stator assembly of the electrical machine 3 while the rotor-stator assembly is in a mounting starting position. The mounting starting position may be the removal end position of the previously removed active stator part, for example a position close to a 12 o'clock position. The opening of the stator may specifically be provided by removing the damaged active stator part. The method may further comprise mechanically connecting the stator 33 to the supporting structure 43, and mechanically disconnecting the stator 33 and the rotor 31. Once the (damaged) stator active part has been replaced, then the stator 33 may be separated from the rotor 31 such that the rotor 31 can rotate again while the stator 33 remains in its place without rotating.

[0062] The method may further comprise rotating the rotor-stator assembly from the mounting starting position to a mounting end position before mechanically connecting the stator 33 to the supporting structure 43 of the stator. The mounting end position may be the removal starting position for that active stator part. If more than one active stator part is replaced, the rotor-stator assembly may be rotated to its final position once all the new active stator parts have been arranged in the stator 33. The step of mechanically connecting the stator 33 to its supporting structure 43 may be performed after rotating the rotor assembly to the mounting end position.

[0063] The method may further comprise applying a force on the stator 33 to align the stator 33 and the supporting structure 43, e.g. axially, and then mechanically connecting the stator 33 and the supporting structure 43. This step may be performed additionally or alternatively to the step of tensing one or more connection tools 35.

[0064] For example, the step of providing one or more tensioned connection tools 35 may be omitted, and the stator 33 may be moved, e.g. pushed upwards, in order to align the stator 33 with its supporting structure(s) 43. One or more lifting devices, e.g. hydraulic jacks, may be used for this.

[0065] Mechanically disconnecting the generator stator 33 from the rotor 31 may comprise removing the one or more connection tools 35 arranged between the rotor 31 and the stator 33 of the rotor-stator assembly. Once the rotor-stator assembly has been moved to the mounting end position, the rotor 31 may be locked, and the connection tools 35 used may be removed. In some examples, the connection tools 35 may be first detached from the stator 33 and then from the rotor 31.

[0066] Required ventilations tubes, cabling, wires, sensors and others may be connected again after the stator 33 is attached to its supporting structure(s) 43. The rotor 31 may be unlocked and rotated on its own again.

[0067] As already mentioned, the electrical machine may be a generator, and in particular a generator of a direct drive of a wind turbine.

[0068] Still in a further aspect, a method 115 for removing an active stator part 37 of a generator 3 of a direct drive wind turbine 10 is provided. An example of this method is shown in the flowchart of figure 9. The method comprises, at block 116, mechanically connecting a rotor 31 of the generator 3 and a stator 33 of the generator 3 to obtain a rotor-stator assembly. The method further comprises, at block 117, mechanically disconnecting the stator 33 from a stator supporting structure 43 such that the rotor-stator assembly is rotatable. The method further comprises, at block 118, rotating the rotor-stator assembly such that the active stator part 37 is accessible. And the method further comprises, at block 119, removing the active stator part 37 from the stator 33.

[0069] Details and explanations of the previous aspects are applicable to this aspect too.

[0070] In some examples, the rotor 31 may be a permanent magnet rotor and the method may further comprise removing one or more of the permanent magnets before mechanically connecting the rotor 31 and the stator 33 to obtain the rotor-stator assembly. If the permanent magnets are provided in modules of permanent magnets, one or more modules may be removed.

[0071] The rotor-stator assembly may be rotated by wind action on one or more blades 22 of the direct drive wind turbine 10. The rotation of the rotor-stator assembly may be controlled bybraking the generator rotor 31 of the direct drive wind turbine 10 and by pitching one or more blades 22 of the direct drive wind turbine 10.

[0072] This written description uses examples to disclose the teaching, including the preferred embodiments, and also to enable any person skilled in the art to practice the teaching, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Claims

CLAIMS1. A method (100) for servicing an active stator part of an electrical machine, the method comprising:mechanically connecting (101) a rotor (31) of the electrical machine and a stator (33) of the electrical machine to obtain a rotor-stator assembly;mechanically disconnecting (102) the stator (33) from a supporting structure (43) such that the rotor-stator assembly is rotatable;rotating (103) the rotor-stator assembly such that the active stator part (42) is accessible; andservicing (104) the active stator part (42).

2. The method of claim 1 , wherein servicing (104) the active stator part comprises removing the active stator part (42) from the stator (33).

3. The method according to claim 1 or claim 2, further comprising introducing one or more connection tools (35) between the rotor (31) and the stator (33) before mechanically connecting (101 ) the rotor and the stator.

4. The method according to claim 3, wherein the one or more connection tools (35) have a partial wedge shape.

5. The method according to claim 3 or 4, wherein the connection tools (35) are arranged in a radial air gap (44) of the electrical machine.

6. The method according to any of claims 3 - 5, the method further comprising locking the rotor (31) after introducing the one or more connection tools (35) and before connecting the rotor (31) and the stator (33).

7. The method according to any of claims 3-6, wherein a first connection tool and a second connection tool of the one or more connection tools (35) are introduced at diametrically opposite locations of the electrical machine.

8. The method according to any of claims 3-7, wherein a first connection tool and a second connection tool of the one or more connection tools (35) are introduced in an upper half of the electrical machine.

9. The method according to any of claims 3 - 8, further comprising creating one or more spaces by removing one or more active rotor parts (37) of the rotor (31), and then introducing the connection tools (35) in the spaces.

10. The method according to any of claims 3 - 9, wherein the one or more connection tools (35) are tensioned to compensate for gravity action on the stator (33) when mechanically disconnecting the stator (33) from the supporting structure (43).

11. The method according to claim 1 or 2, wherein the rotor (31) of the electrical machine is connected to the stator (33) of the electrical machine to obtain a rotor-stator assembly at an upwind side or at a downwind side of the electrical machine, at least partially outside a radial air gap (44) of the electrical machine.

12. The method according to any of claims 1 - 11, wherein the electrical machine is a generator (3).

13. The method according to claim 12, wherein the generator (3) is a generator of a direct drive wind turbine (10).

14. The method according to claim 13, wherein the rotor-stator assembly is rotated by wind action on one or more blades (22) of the direct drive wind turbine (10).

15. The method according to claim 14, further comprising pitching one or more blades (22) of the direct drive wind turbine (10) and / or braking the generator rotor (31) of the direct drive wind turbine (10) to control the rotation of the rotor-stator assembly.

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