Patent Description:
The airgap, which is formed between the stator and a rotor in a wind turbine electric generator is an important design feature that contributes to determines the overall efficiency of the wind turbine. The tighter the airgap is and the less it fluctuates over the lateral surfaces the axial ends of the stator and the rotor, the more energy can be generated and the higher the efficiency is. During the assembly process of the electric generator, it is known to measure the airgap after the pairing between stator and rotor. The airgap has normally a thickness in the range of some millimetres and is therefore not well accessible. Nevertheless, the production must record the values as part of the quality check. Furthermore, the airgap measurement is possibly provided to the customer as a critical quality reference in the future.

This measurement may be performed manually by technicians, who have to crawl into the inside of the stator and use calliper gauges that are applied through radial airducts in the stator segments to measure the airgap. Multiple measurements are performed along the circumference of the generator. This procedure implies a plurality of inconveniences, for example:.

The document <CIT> discloses a method for performing a plurality of measurements in the air gap between a stator and a rotor of a generator for a wind turbine according to the state of the art.

It may be therefore an object of the present invention to provide a method and a device for measuring the airgap between the stator and the rotor of an electric generator, which overcomes the above-mentioned inconveniences of the prior art.

This object may be solved by a method and a device according to the subject matter of the independent claims.

One aspect of the invention relates to a method for performing a plurality of measurements in the air gap between a stator and a rotor of a generator for a wind turbine, the rotor being rotatable with respect to the stator about a rotational axis, the method including the steps of:.

According to possible embodiments of the invention, said one or more parameter(s) associated with the air gap may be any of:.

The present invention permits to achieve the following advantages:.

It is further possible that the nominal airgap may be reduced in turbine generations due to higher confidence of the airgap, due to the above-described measurement procedure. The production can fulfill quality assurance step faster, with higher data accuracy in less manual work (faster process). It also supports to understand assembly factors better how they impact the airgap and thus optimize the assembly to achieve an optimal airgap.

According to a possible embodiment of the invention, said steps of mounting rotating and measuring are first performed with the plurality of distance measuring sensors mounted on one of the stator and rotor and then said steps of mounting rotating and measuring are again performed with the plurality of distance measuring sensors (<NUM>) mounted on the other of rotor and stator.

According to another possible embodiment of the invention, in said step of mounting a first plurality of distance measuring sensors are mounted on a first surface of the stator and a second plurality of distance measuring sensors are mounted on a second surface of the rotor, said first and second surfaces facing the air gap.

According to possible embodiments of the invention, at least a portion of plurality of distance measuring sensors are fixed to a longitudinal support, said longitudinal support being fixed on a surface of the stator and/or the rotor, said surface facing the air gap, during said step of mounting.

Another aspect of the invention relates to a measurement device for performing a plurality of measurements in the air gap between a stator and a rotor of a generator for a wind turbine, the measurement device including:.

According to possible embodiments of the invention, the longitudinal support may be in form of a stick along which the plurality of sensors is attached. The sensors may be regularly distributed along the length of the longitudinal support. The longitudinal support may be oriented during the measurement operations along the rotational axis of the electric generator or inclined with respect thereto of an inclination angle comprised between <NUM> and <NUM> degree. Such inclination angle may depend on the geometric constraints of the stator and/or rotor. The longitudinal support with the plurality of sensors may be fixed during the measurement operations to a surface of the stator or to a surface of the rotor, such surfaces of the stator and the rotor facing the airgap. In electric generators where the rotor is radial external to the stator, the longitudinal support with the plurality of sensors may be fixed during the measurement operations to an external surface of the stator or to an internal surface of the rotor. In electric generators where the rotor is radial internal to the stator, the longitudinal support with the plurality of sensors may be fixed during the measurement operations to an external surface of the rotor or to an internal surface of the stator. In permanent magnet electric generators, the longitudinal support with the plurality of sensors may be fixed to one or more magnets facing the airgap.

According to possible embodiments of the invention, the measurement device may include two longitudinal supports to be respectively fixed during the measurement operations to a surface of the stator and to a surface of the rotor, such surfaces of the stator and the rotor facing the airgap.

According to possible embodiments of the invention, the longitudinal support with the plurality of sensors may be fixed at positions, which are radially distanced from the airgap.

According to possible embodiments of the invention, the plurality of distance measuring sensors are capacitive sensors. The sensors may be capacitive film sensors or capacitive flat sensors. The sensors may be capacitive tactile sensor or eddy current sensors.

According to possible embodiments of the invention, the longitudinal support is fixed to the stator or the rotor by means of at least one thread or similar thin material. Each thread may grasp the longitudinal support and extend through a respective air duct of the stator, the thread being tightened in such a way that the longitudinal support is pushed against the external side of the stator. Such embodiments permit a strong fixation of the longitudinal support onto the stator surface. The fixing procedure is characterized by easy handability with tightening, removability without destroying materials and reusability.

According to possible embodiments of the invention, the longitudinal support is fixed to the stator or the rotor by applying un under-pressure between the longitudinal support and a surface of the stator or the rotor facing the air gap, the under-pressure pushing the longitudinal support towards the surface of the stator or the rotor facing the air gap. In such embodiments, the longitudinal support may comprise a channel having an opening to be attached to a surface of the rotor facing the air gap, the measurement device comprising an under-pressure generator to be connected to the channel for evacuating air is activated, air can be evacuated from the opening. Fixing by applying under-pressure allows secure and strong fixation of the longitudinal support onto a rotor surface, e.g. a magnet surface. Removability without destroying materials and reusability can be achieved. A thin design is possible for adapting to the tight space conditions in the airgap.

It should be understood that features, which have individually or in any combination been disclosed for a method for performing a plurality of measurements in the air gap between a stator and a rotor of a generator for a wind turbine, may also, individually or in any combination, be provided for a measurement device according to embodiments of the present invention and vice versa.

<FIG> shows a wind turbine <NUM> according to the invention. The wind turbine <NUM> comprises a tower <NUM>, which is mounted on a non-depicted foundation. A nacelle <NUM> is arranged on top of the tower <NUM>. The wind turbine <NUM> further comprises at least a wind rotor <NUM> having a hub and at least one blade <NUM> (in the embodiment of <FIG>, the wind rotor comprises three blades <NUM>, of which only two blades <NUM> are visible). The wind rotor <NUM> is rotatable around a rotational longitudinal axis Y. The blades <NUM> extend substantially radially with respect to the longitudinal rotational axis Y. In general, when not differently specified, the terms axial, radial and circumferential in the following are made with reference to the longitudinal rotational axis Y. The wind turbine <NUM> comprises at least one electric generator <NUM>, including a stator <NUM> and a rotor <NUM>. The rotor <NUM> is rotatable with respect to the stator <NUM> about the longitudinal rotational axis Y. The wind rotor <NUM> is coupled with the rotor <NUM>, in order to rotate about the rotational longitudinal axis Y. The electric generator <NUM> comprise an airgap <NUM> radially interposed between the stator <NUM> and the rotor <NUM>, the airgap <NUM> extending circumferentially about the rotational axis Y. In the embodiment of the attached figures the rotor <NUM> is radially external to the stator <NUM>. According to other embodiments (not show), the rotor may be radially internal to the stator.

<FIG> shows an exploded view of the electrical generator <NUM> with the rotor <NUM> and the stator <NUM>. The stator <NUM> comprises a cylindrical inner core to which six segments <NUM> are attached. Each segment <NUM> has a circumferential angular extension of <NUM>°. According to other embodiments of the present invention, the stator <NUM> comprises a plurality of segments having a number of segments different from six. According to another possible embodiment of the present invention, the stator <NUM> is not segmented, i.e. the stator includes one single segment covering the entire angular extension of <NUM>°. The rotor <NUM> has a conventional structure with a plurality of circumferentially distributed rotor permanent magnets <NUM>. The magnets <NUM> are distributed on an inner side of the rotor <NUM> according to axial columns. Each column of magnets comprises a plurality of magnets <NUM> (two magnets <NUM> in the embodiment of <FIG>) aligned along the rotational axis Y.

<FIG> show two respective block diagram of a method <NUM> for performing a plurality of measurements in the air gap <NUM>. Such method may be performed during the manufacturing of the electric generator, for example as quality check.

A method <NUM> for performing a plurality of measurements in the air gap <NUM> includes the following steps:.

Such parameter(s) associated with the air gap <NUM> may be one or more of:.

<FIG> shows a first embodiment of a block diagram of a method <NUM>. In a first execution of the first step <NUM>, the method <NUM> comprises mounting a plurality of distance measuring sensors <NUM> on a surface of the stator <NUM> facing the air gap <NUM> (<FIG> and <FIG>). For example, the sensors <NUM> may be attached to an external surface of a stator segment <NUM>. The plurality of distance measuring sensors <NUM> may be alternatively mounted on a surface of the rotor <NUM> facing the air gap <NUM>. The sensors <NUM> are fixed to the stator <NUM> or rotor <NUM> in such a way that each distance measuring sensor <NUM> is distanced from the other distance measuring sensors <NUM> along the rotational axis Y. After the first step <NUM> the rotor <NUM> and the stator <NUM> are paired and a break disc <NUM> (shown in <FIG>) is attached to the generator <NUM>. In a first execution of the second step <NUM> the method <NUM> comprises rotating the rotor <NUM> about the rotational axis Y. A complete rotation of <NUM> degrees or more may be executed. The rotation of the rotor <NUM> is initiated and stopped by an external device. In a first execution of the third step <NUM> of the method <NUM> comprises, while rotating the rotor <NUM>, measuring a first plurality of distances between each of the distance measuring sensors <NUM>, which has been mounted during the first step <NUM> of the method, and respective facing points across the air gap <NUM>. After the third step <NUM> the sensors <NUM>, which have been mounted during the first execution of the first step <NUM>, are removed. The first step <NUM> of the method <NUM> is then repeated mounting the same or another plurality of distance measuring sensors <NUM> on a surface of the rotor <NUM> facing the air gap <NUM> (<FIG>). For example, the sensors <NUM> may be attached to the magnets <NUM>. The plurality of distance measuring sensors <NUM> may be alternatively mounted on a surface of the stator <NUM> facing the air gap <NUM>, if in the previous execution of the first step <NUM> distance measuring sensors <NUM> were mounted on the rotor <NUM>. A second execution of the second step <NUM> and third step <NUM> is also performed for measuring a second plurality of distances by means of the distance measuring sensors <NUM>. After the third step <NUM> the sensors <NUM>, which have been mounted during the second execution of the first step <NUM>, are removed and the final fourth step <NUM> is performed.

<FIG> shows a second embodiment of a block diagram of a method <NUM>. In the first step <NUM>, the method <NUM> comprises mounting a first plurality of distance measuring sensors <NUM> on a surface of the stator <NUM> facing the air gap <NUM> (<FIG>). For example, the sensors <NUM> may be attached to an external surface of a stator segment <NUM>. The rotor <NUM> and the stator <NUM> are then paired. In the first step <NUM>, the method <NUM> further comprises mounting a second plurality of distance measuring sensors <NUM> on a surface of the rotor <NUM> facing the air gap <NUM>. For example, the sensors <NUM> may be attached to the magnets <NUM>. The sensors <NUM> are fixed to the stator <NUM> and rotor <NUM> in such a way that each distance measuring sensor <NUM> is distanced from the other distance measuring sensors <NUM> along the rotational axis Y. After that the break disc <NUM> is attached to the generator <NUM>. The second step <NUM> of the method <NUM> is executed by rotating the rotor <NUM> about the rotational axis Y. A complete rotation of <NUM> degrees or more may be executed. The rotation of the rotor <NUM> is initiated and stopped by an external device. The third step <NUM> of the method <NUM> is then executed, while rotating the rotor <NUM>, for measuring a plurality of distances between each of the distance measuring sensors <NUM>, which has been mounted during the first step <NUM> of the method, and respective facing points across the air gap <NUM>. The plurality of distances measured during the third step <NUM> includes the measurement performed with the first plurality of sensors <NUM> and the second plurality of sensors <NUM> installed during the first step <NUM>. After the third step <NUM> the sensors <NUM> are removed and the final fourth step <NUM> is performed.

<FIG> shows the coupling between a plurality of sensors <NUM> and a segment <NUM> of the stator <NUM>, performed during the first step <NUM> of the method <NUM>. The distance measuring sensors <NUM> are comprised in a measurement device <NUM>, which also includes a longitudinal support <NUM>, for example a stick, on which the sensors <NUM> are fixed and a controller <NUM> connected to the plurality of distance measuring sensors <NUM>, for example by means of a cable <NUM>, and configured for performing the steps of the method <NUM>. The measurement device <NUM> of <FIG> includes six distance measuring sensors <NUM>. According to other embodiments (not shown), the measurement device <NUM> of <FIG> may include two or more distance measuring sensors <NUM>. The measuring sensors <NUM> may be capacitive sensors. For example, the measuring sensors <NUM> may be capacitive film sensors or capacitive flat sensors. According to other embodiments (not shown), the longitudinal support <NUM> may include one or more cable ties, screws, rubber bands, a knee-lever system or similar. The longitudinal support <NUM> may be tightened on the outer surface of the segment <NUM> with any tightening means.

<FIG> shows the pairing between the stator <NUM> and the rotor <NUM> and the mounting of the break disc <NUM>, performed after the first execution of the step <NUM> in the first embodiment (<FIG>) of the method <NUM>.

<FIG> shows the coupling between a plurality of sensors <NUM> and the rotor <NUM>, performed during the second execution of the first step <NUM> in the first embodiment (<FIG>) of the method <NUM>. The distance measuring sensors <NUM> are comprised in the same measurement device <NUM> used during the first execution of the step <NUM> (<FIG>) or in another measurement device <NUM>. In other to facilitate the coupling between the measuring sensors <NUM> and the magnets <NUM>, the longitudinal support <NUM> comprises a metallic material that has low magnetic properties. The length of the longitudinal support <NUM> may be in the range of some. A correct positioning may therefore require a guide for the longitudinal support <NUM>.

<FIG> shows a guide <NUM> temporarily attached to the break disc <NUM> for introducing the longitudinal support <NUM> and the plurality of sensors <NUM> to be attached to the rotor <NUM> through an inspection hole <NUM> of the break disc <NUM>. The longitudinal support <NUM> is inserted through the guide <NUM> and the inspection hole <NUM> of the break disc <NUM> and mounted on the rotor <NUM> with an angle of inclination α, which may be comprised between <NUM> and <NUM> degrees with respect to the rotational axis Y. the angle of inclination α depends on the geometrical constraints of the assembly including the stator <NUM> and the rotor <NUM>.

According to other embodiments (not shown), the break disc <NUM> is not mounted when the longitudinal support <NUM> is to be coupled to the rotor <NUM>, for example during the first step <NUM> in the second embodiment (<FIG>) of the method <NUM>. In such case another component of the electric generator <NUM> may be used for mounting the guide <NUM>.

<FIG> and <FIG> show more in detail, with respect to <FIG>, the coupling between a plurality of sensors <NUM> fixed on the longitudinal support <NUM> and a segment <NUM> of the stator <NUM>. The segment <NUM> comprises a plurality of segment axial portions <NUM> which are arrayed along the longitudinal or rotational axis Y. The segment axial portions <NUM> are separated from each other by air ducts <NUM> for letting a cooling fluid flow in the air duct <NUM>. Each segment axial portion <NUM> may be formed of a plurality of laminations stacked along the longitudinal axis Y to form the segment <NUM>. At each air duct <NUM> the lamination stack is discontinued, and a plurality of spacers <NUM> are provided in the air duct <NUM> between the two respective and axially adjacent segment axial portions <NUM>. The measurement device <NUM> comprises one or more threads <NUM> (six threads <NUM> in the embodiment shown in <FIG>), each thread <NUM> extending through a respective air duct <NUM>. The thread <NUM> grasps the longitudinal support <NUM> and is tightened in such a way that the longitudinal support <NUM> is pushed against the external side of the stator segment <NUM> (<FIG>). On the opposite internal side of stator segment <NUM> (<FIG>) a respective thread tightener <NUM> is provided to tighten the thread <NUM>. The thread <NUM> may be made on nylon or other similar material. According to other embodiments of the invention, threads <NUM> may be used to to fix the longitudinal support <NUM> to the rotor <NUM>.

Claim 1:
A method for performing a plurality of measurements in the air gap (<NUM>) between a stator (<NUM>) and a rotor (<NUM>) of a generator (<NUM>) for a wind turbine (<NUM>), the rotor (<NUM>) being rotatable with respect to the stator (<NUM>) about a rotational axis (Y), the method including the steps of:
mounting a plurality of distance measuring sensors (<NUM>) on at least one surface of the stator (<NUM>) and/or the rotor (<NUM>), said surface facing the air gap (<NUM>), each distance measuring sensor (<NUM>) being distanced from the other distance measuring sensor(s) (<NUM>) along the rotational axis (Y),
rotating the rotor (<NUM>) about the rotational axis (Y),
while rotating the rotor (<NUM>), measuring a plurality of distances between each of said distance measuring sensors (<NUM>) and respective facing points across the air gap (<NUM>),
deriving from said plurality of distances one or more value(s) of one or more parameter(s) associated with the air gap (<NUM>) and/or the stator (<NUM>) and/or rotor (<NUM>), characterized in that at least a portion of plurality of distance measuring sensors (<NUM>) are fixed to a longitudinal support (<NUM>), said longitudinal support (<NUM>) being fixed on a surface of the stator (<NUM>) and/or the rotor (<NUM>), said surface facing the air gap (<NUM>), during said step of mounting.