DK201770174A1 - Wind turbine component thermal monitoring - Google Patents

Abstract

A method of controlling the operating temperature of a wind turbine transformer is provided. The method comprises acquiring (610) data indicative of the operating temperature of the wind turbine transformer using at least one optical temperature sensor (425) located at a distance from the transformer and positioned to detect the temperature of at least a portion of the transformer. The method further comprises operating one or more transformer cooling devices based on the operating temperature to cool the transformer and/or altering the power applied to the transformer based on the operating temperature (660).

Description

(19) DANMARK <¹°> DK 2017 70174 A1

<¹²> PATENTANSØGNING

Patent- og

Varemærkestyrelsen (51)

Int.CI.: F03 D 17/00 (2016.01)

F 03 D 80/60 (2016.01)

H 01 F 27/08 (2006.01) (21) Ansøgningsnummer: PA 2017 70174 (22) Indleveringsdato: 2017-03-10 (24) Løbedag: 2017-03-10 (41) Aim. tilgængelig: 2018-01-09 (71) Ansøger: VESTAS WIND SYSTEMS A/S, Hedeager 42, 8200 Århus N, Danmark (72) Opfinder: Jesper Hillebrandt, Pugflodsvej 10, 6950 Ringkøbing, Danmark (74) Fuldmægtig: Vestas Wind Systems A/S IPR Department, Hedeager 42, 8200 Århus N, Danmark (54) Benævnelse: WIND TURBINE COMPONENT THERMAL MONITORING (56) Fremdragne publikationer:

US 7834472 B2 US 2013181451 A1 GB 1470692 A WO 2013096237 A1 US 2006250683 A1 GB 1048025 A US 2012124984 A1 EP 3098442 A1 EP 2151833 A1 EP 2821642 A1 CN 202817564 U (57) Sammendrag:

A method of controlling the operating temperature of a wind turbine transformer is provided. The method comprises acquiring (610) data indicative of the operating temperature of the wind turbine transformer using at least one optical temperature sensor (425) located at a distance from the transformer and positioned to detect the temperature of at least a portion of the transformer. The method further comprises operating one or more transformer cooling devices based on the operating temperature to cool the transformer and/or altering the power applied to the transformer based on the operating temperature (660).

Fortsættes ...

DK 2017 70174 A1

FIG. 4

DK 2017 70174 A1

WIND TURBINE COMPONENT THERMAL MONITORING

Field of Invention

The present invention relates to monitoring the temperature of wind turbine components, and particularly wind turbine transformers.

Background

Figure 1 illustrates a large modern wind turbine 10 as known in the art, comprising a tower 11 and a wind turbine nacelle 13 positioned on top of the tower. Wind turbine blades 15 of a turbine rotor 12 are mounted on a common hub 14 which is connected to the nacelle 13 through the low speed shaft extending out of the nacelle front. The wind turbine blades 15 of the turbine rotor 12 are connected to the hub 14 through pitch bearings 16, enabling the blades to be rotated around their longitudinal axis. The pitch angle of the blades 15 can then be controlled by linear actuators, stepper motors or other means for rotating the blades. The illustrated wind turbine 10 has three turbine blades 15, but it will be appreciated that the wind turbine could have another number of blades such as one, two, four, five or more.

The wind turbine may also include a wind turbine controller, located on or within the turbine, or at a remote location from the turbine. The controller may be communicatively coupled to any number of the components of the wind turbine in order to control them. The controller may be a computer or other suitable processing unit. For example, the controller could include software that, when executed, causes the controller to perform various functions, such as receiving, transmitting and/or executing wind turbine control signals and the various method steps described herein. The controller may include a communications module to allow communications between the controller and the various components of the wind turbine. A sensor interface (e.g. one or more analogue-to-digital converters) may be included to convert sensor signals into signals that can be processed by the controller.

Figure 2 illustrates a simplified cross section of an example nacelle 13 of a wind turbine 10, as seen from the side. The nacelle 13 exists in a multitude of variations and configurations but in most cases comprises one or more of the following components: a gearbox 130, a coupling (not shown), some sort of braking system 131 and a generator 132. A nacelle can also include a converter 133 (also called an inverter) and additional peripheral equipment

DK 2017 70174 A1 such as further power handling equipment, control cabinets, hydraulic systems, cooling systems and more.

Typically, a wind turbine generator is connected to a step-up transformer which increases the turbine generator voltage. These transformers may be located in the nacelle of the wind turbine, or at another nearby location, such as near the base of the turbine tower. Oil filled transformers or dry type transformers may be used, for example.

Transformers generally consist of two or more winding sets. The winding set(s) connecting to the grid can be defined as the high voltage coils (HV) and typically have a highest equipment voltage in the range of 7.2 kV < Urn < 72.5 kV. The winding set(s) connecting to the turbine can be defined as the low or medium voltage coils, with low voltage coils typically having a highest equipment voltage below 1 kV, and medium voltage coils in the range of 1 < Urn < 7.2 kV.

The turbine cooling system may be comprised of one or more cooling devices, which may otherwise be known as cooling means, cooling components and so on. Various cooling devices may be configured with associated components of the wind turbine. Critical components may be provided with their own dedicated cooling devices. Critical components include converters and/or transformers, but may also include other components such as the generator and/or gearbox.

The cooling devices may be cooling fans. Such fans may be configured to direct cool air across or through the internal components of the component in question in order to maintain the component temperatures within predetermined limits. The fans may be variable speed fans, the speed of the fan being increased to increase cooling effect and decreased to decrease cooling effect. The fan speed may be controlled by the wind turbine controller, or by a separate control system. Fan speed may be controlled as a function of one or more operating parameters and conditions that correlate to component temperature, such as the temperature of the corresponding component that the fan is cooling.

One or more cooling devices, such as cooling fans, may be included in a wind turbine to maintain operating temperatures within design limits. For example, a transformer, gearbox, power converter and/or the generator may include one or more cooling fans. A general cooling fan for the turbine nacelle environment may also be present.

DK 2017 70174 A1

An object of embodiments of the present invention may be to provide a method of more reliably monitoring the temperature of wind turbine transformers and to control cooling of the transformers.

Summary of the Invention

The invention is defined in the independent claims to which reference should now be made. Preferred features are detailed in the dependent claims.

According to a first aspect, the invention provides a method of controlling the operating temperature of a wind turbine transformer. The method comprises acquiring data indicative of the operating temperature of the wind turbine transformer using at least one temperature sensor located at a distance from the transformer and positioned to detect the temperature of at least a portion of the transformer. The method further comprises: operating one or more transformer cooling devices based on the operating temperature to cool the transformer; and/or altering the power applied to the transformer based on the operating temperature. Altering the power applied to the transformer protects the transformer from operating at excessive temperatures, for example by reducing or disconnecting power based on the obtained temperature.

The inventors have appreciated that by using a remote temperature sensor that is configured to measure the temperature of a surface at a distance from the sensing element without requiring physical contact of any part of the temperature sensor with the surface, it is possible to accurately monitor the temperature of parts of the wind turbine transformer that might not be capable of being monitored using traditional methods. This therefore provides greater flexibility in temperature monitoring, allowing control strategies for cooling devices to better take into account the temperature of specific parts of the transformer.

The temperature sensor may be a remote infra-red sensor, such as a pyrometer or a sensor arrangement that uses infrared imaging, for example.

Optionally, the transformer comprises high voltage coils and low or medium voltage coils, and the at least one temperature sensor is positioned to detect a temperature of the high voltage coils. The at least one temperature sensor may, in particular, be positioned to detect a surface temperature of the high voltage coils.

Although traditional wired temperature monitoring devices such as PT100 sensors and thermocouples can be inserted directly into the low voltage (LV) or medium voltage (MV)

DK 2017 70174 A1 coils of a transformer, the inventors have appreciated that this is not possible for the high voltage (HV) coils. The high voltage level, and risk of partial discharges in the high voltage coil insulation material and flashover to wiring of the temperature monitoring device, mean that there is a risk of damage to control equipment as well as personal injury. This can lead to inaccurate temperature sensing and premature thermal failure. Rather than use typical temperature monitoring devices, it has been appreciated that using a remote temperature sensor that provides touch free temperature monitoring allows the temperature of the high voltage coils to be taken into account in a temperature control scheme in a safe and reliable manner. The thermal constant of the high voltage coil is higher than that of the low or medium voltage coil, and its temperature rise can be greater than that of the low or medium voltage coil. There is therefore a risk that the temperature of the high voltage windings exceeds safe levels when cooling is controlled based solely on signals from the colder and thermally faster-responding low or medium voltage coils.

Embodiments can offer improved thermal protection of the transformer and improve thermal insulation lifetime by ensuring cooling systems are kept in operation when high voltage coils are hot, without relying only on low or medium voltage coil temperature measurements. This is especially important for turbines installed at high altitude sites where cooling is less efficient, and where it is important to provide good thermal management of the components to prevent premature failures.

Optionally the method further comprises acquiring data indicative of the operating temperature of the low or medium voltage coils of the transformer using at least one further temperature sensor; and controlling operation of the one or more transformer cooling devices, and/or altering the power applied to the transformer based on the detected temperature, based on the operating temperature of the high voltage and low or medium voltage coils. Optionally the one or more transformer cooling devices are operated based upon the detected temperature of the high voltage coils independently to the detected temperature of the low or medium voltage coils. Optionally the power applied to the transformer from the wind turbine is controlled based upon the detected temperature of the high voltage coils independently to the detected temperature of the low or medium voltage coils.

According to a second aspect, a controller for controlling a wind turbine or a wind power plant is provided, the controller being configured to carry out any of the methods described

DK 2017 70174 A1 herein. A turbine comprising such a controller, or a wind power plant featuring such a controller, may also be provided.

According to a third aspect there may be provided a wind turbine comprising a transformer coupled to the wind turbine generator; and at least one temperature sensor located at a distance from the transformer and positioned to detect the temperature of at least a portion of the transformer, the temperature sensor being coupled to a controller configured: to control the cooling applied to the transformer; and/or to alter the power applied to the transformer based on the detected temperature.

Optionally the transformer comprises high voltage coils and low or medium voltage coils, and wherein the at least one sensor is positioned to detect a temperature of the high voltage coils. Optionally the at least one temperature sensor is positioned to detect a surface temperature of the high voltage coils. Optionally the transformer comprises three or more elements corresponding to different phases, with at least one first element arranged between two other elements, and wherein the at least one temperature sensor is positioned to detect a temperature of the high voltage coil of the first element of the transformer.

Optionally the wind turbine comprises at least one further temperature sensor positioned to detect a temperature of the low or medium voltage coils.

Optionally the temperature sensor is an optical temperature sensor, such as an infra-red temperature sensor.

Optionally the sensing element of the temperature sensors are located between 200mm and 1000mm from the transformer.

A computer program may also be provided that, when executed on a computing device, causes it to carry out any of the methods described herein.

Brief Description of the Drawings

Examples of the invention will now be described in more detail with reference to the accompanying drawing in which:

Figure 1 illustrates a large modern wind turbine;

DK 2017 70174 A1

Figure 2 illustrates a simplified cross section of a wind turbine nacelle, as seen from the side;

Figure 3 illustrates an example of a wind turbine transformer arrangement;

Figure 4 illustrates an example of an embodiment of the invention;

Figure 5 illustrates a control system in accordance with an embodiment of the invention; and

Figure 6 illustrates a method in accordance with an embodiment of the invention.

Detailed Description of Preferred Embodiments

An example of the invention will now be described in relation to a dry-type high voltage wind turbine transformer. Embodiments of the invention may be applied to other types of transformer.

Figure 3 shows an example of a high voltage dry-type transformer for use in a wind turbine. Three transformer elements 301a, 301b and 301c are provided for each phase. Each transformer element includes the LV coil windings 304 and the HV coil windings 305. A common three-leg core 306 is provided that provides the transformer core for each of the elements 301a, 301b and 301c. The LV coil windings are each connected to corresponding LV terminals 306a, 306b and 306c. The HV coil windings are similarly each connected to corresponding HV terminals but these are not shown in the figure. A frame or mount 310a, 310b may be provided on which the components are fixed for mounting into a housing in the nacelle or at the tower base. The transformer elements may be attached to the frame by resilient spacers, for example.

The high voltage transformer of a wind turbine may be used to step up the voltage from the generator to the grid voltage. As an example, a generator voltage of around 690V may be stepped up to 10 to 36 kV. The generator voltage level will depend upon the wind turbine design.

Temperature monitoring of the transformer windings is used to control the turbine cooling systems for the transformer. Temperature monitoring devices can be inserted directly into

DK 2017 70174 A1 the LV coils. However, the same is not true of the HV coils. The high voltage level, and risk of partial discharges in the HV coil insulation material and flashover to wiring of the temperature monitoring device, mean that there is a risk of damage to control equipment, as well as personal injury, if conventional temperature monitoring devices are used. Furthermore, inserting temperature monitors into the HV coils may alter the uniformity/homogeneity of the insulation system.

The thermal constant of the HV coil is lower than that of the LV coil, and its temperature rise can be greater than that of the LV coil. There is therefore a danger that the temperature of the HV coils could exceed safe levels when cooling is controlled based solely on signals from the colder and faster-responding LV coils.

A temperature sensor, such as an infra-red (IR) sensor, is located remotely from the transformer and is used to provide touch-free temperature sensing. The signal from the sensor, containing information indicative of the temperature of the HV coils of a wind turbine transformer, is sent to a control system. The signal provided to the control system may be an analogue signal which is converted to a digital signal at, or prior to, the control system. Alternatively the sensor may output a digital signal, depending upon the type of sensor used.

The temperature sensor is installed a safe distance from the surface of the HV coils. For example, the sensor may be installed such that the sensing element is positioned anywhere from 200mm to 1000mm from the HV windings surface, and is oriented to detect a temperature of a region of the surface of the HV windings. The sensor may be any appropriate touch free or non-contact sensor, such as a non-contact thermometer, an infrared camera, an infrared sensor, or a pyrometer. Preferably the sensor has an analogue output signal.

The signal indicative of the temperature of the HV coils may be complimentary to temperature sensing performed in relation to the LV coils, and can be used in the same control functionality to provide a higher degree of thermal protection of the transformer.

Figure 4 shows the example transformer of Figure 3 when mounted within the wind turbine nacelle 421. Figure 4 is a sectional view, taken along the rotational axis of the blade and omitting some features of the turbine, for example the figure shows only one side of the nacelle wall. The transformer may be mounted on a plate or frame (not shown) within the nacelle, and is electrically connected to the generator (not shown).

DK 2017 70174 A1

A temperature sensor 425 is mounted in a position remote from the transformer. In the example of Figure 4 the sensor is mounted on the interior of the nacelle housing and is orientated to measure the temperature on at least a portion of the surface 427 of the transformer. In particular, the sensor may be orientated to measure the temperature on a portion of the HV coils of one or more of the transformer elements.

In this example the central transformer element 301b, located between two outer elements 301a and 301c, is selected as the target for the temperature sensor because its HV coils are likely to operate at a slightly higher temperature than the outer elements. This is due to factors such as reduced air flow and increased heating caused by the elements positioned either side. However, the optical temperature sensor may be orientated to measure the surface temperature of any of the transformer elements.

A plurality of temperature sensors may be provided, each orientated to measure the temperature of at least a portion of the surface of respective elements of the transformer. Each of the temperature sensors may be mounted on the nacelle, or sensors may be mounted in different locations as appropriate, depending upon the portion of the HV windings that are being targeted. A combination of the measurements from the HV coil sensors may then be used in the cooling control system. For example, for the purposes of temperature control the highest value, or an average value, from the sensors may be used.

The specific example described in relation to Figures 3 and 4 is a three phase transformer. It will be appreciated that three individual single phase transformers could be used instead. It will also be appreciated that if the wind turbine output is fewer than three phases, a corresponding transformer arrangement, or corresponding number of individual phase transformers, may be used. The number of HV temperature sensors used may be at least equal to the number of phases used in the wind turbine generator, or at least equal to the number of independent HV coils used in the transformer arrangement. For the avoidance of doubt, however, one or more sensors may be used, with no upper limit on the number.

In the example above the transformer is mounted within the turbine nacelle. Alternatively, the transformer may be located in a housing outside the turbine, such as proximate to the base of the turbine tower. In this case the housing would replace the nacelle in the description above.

Figure 5 is a diagram showing an example of the relationship between components of the wind turbine. The transformer 300 is shown with a sensor system comprising a HV

DK 2017 70174 A1 contactless temperature sensor 425. A LV sensor 534 may also be provided as part of the sensor system. As described above there may be more than one HV sensor as appropriate, and there may also be more than one LV sensor.

The output from the sensor system is provided to the wind turbine controller 530. The wind turbine controller receives data from the sensor system and based on the received data controls an operating parameter of a wind turbine cooling system 532. The term “operating parameter” refers to any parameter of the wind turbine cooling system which affects the level of cooling provided by the cooling system to the transformer.

The cooling system 532 may comprise one or more cooling devices such as one or more fans positioned around or within the transformer 300 so as to provide cooling. The cooling systems may be positioned and oriented to provide cooling to specific portions of the transformer, such as the surfaces of the HV coils.

The controller 530 provides a control signal, such as a voltage or current signal, to one or more of the cooling devices within the cooling system 532 to alter the level of cooling provided based upon the determined temperature of the HV and LV coils.

The wind turbine controller may also perform other control functions with respect to the wind turbine, such as controlling one or more turbine operating parameters based on data 536 received from other turbine or wind park sensors via one or more control signal outputs 538. An example of such an additional function would be controlling turbine operating parameters such as blade pitch and/or rotor yaw to maximise, or alter, power generation.

In other embodiments the controller 530 may be a dedicated cooling system controller.

Figure 6 provides an example of a method for controlling the temperature of a wind turbine controller, and may be used in accordance with any of the arrangements described herein.

At step 610 the output of the temperature sensor associated with the HV coil is acquired. A determination is then made, at step 620, of the HV winding temperature based on the sensor output. This temperature value can then be used in a feedback loop to control one or more cooling devices to maintain the transformer temperature below a predetermined value, or within a predetermined operational temperature range. The temperature value can also, or alternatively, be used to stop the turbine or disconnect the transformer in case the value exceeds predefined limits.

DK 2017 70174 A1

The determination of the HV winding temperature may be performed by taking the temperature value from the sensor output to be the HV winding temperature. However, as described herein the temperature measurement will apply to the portion of the surface of the HV windings covered by the sensor, and this may not be the same as the temperature of the remainder of the transformer windings. Therefore the measurement of surface temperature may be converted or mapped to a value indicative of the temperature of the rest of the windings, or an average temperature of the windings as a whole. This may be performed using a predetermined mapping function or look-up table established during a testing phase, by measuring the corresponding temperatures of the remainder of the HV winding for a given sensor measurement over a particular region. The test measurements may be performed with any appropriate sensor, including an optical temperature sensor.

In another example, the determination of the HV winding temperature may be performed for two or more HV sensor outputs. As described above, these sensors may be oriented to detect the surface temperature for different phases of HV windings, and/or for different portions of the same HV winding. The various sensed temperature values may then be processed individually, in the same manner as described above, or they may be combined into a single temperature value and processed at the same time. For example, an average value may be taken of the various temperatures, which may be appropriately weighted to account for the position of one HV winding phase with respect to the others. For example, if transformer element 301b were known to run at a higher operating temperature than elements 301a and 301c then a higher weighting may be applied to the temperature of this winding as it is at risk of higher thermal damage.

Continuing with Figure 6, at step 630 the determined transformer HV winding temperature is compared to a predetermined temperature or temperature range. The predetermined temperature or temperature range may be based upon manufacture recommendation information, or predetermined measured or modelled data that indicates a safe operating temperature, or operating temperature range, for the HV coils. If the temperature indicated at step 620 is beyond the safe operating parameters of the transformer HV windings then one or more cooling devices are adjusted to increase the amount of cooling provided, so as to decrease the operating temperature of the HV windings.

At step 660 the associated cooling fan or fans for the transformer is/are operated at the speed/RPM required to satisfy the cooling requirements associated with the temperature, so as to keep the operating temperature of the HV windings within their operating range.

DK 2017 70174 A1

The required speed of the fan may be determined based upon a predetermined relationship with the temperature of the high voltage coils, for example. This step may be performed by the wind turbine controller, or may be performed by a different system such as a controller of a cooling system.

As an alternative to, or in addition to, step 660, the power applied to the transformer by the turbine may be altered based on the operating temperature. The power may be altered by reducing wind turbine power, e.g. by altering turbine blade pitch, or by disconnecting power applied from the turbine to the transformer. This may be performed by a turbine power control system.

Control of the cooling device may, at the same time, be implemented independently based upon the temperature values determined by one or more LV temperature sensors. The LV temperature sensor(s) are used to determine the LV winding temperature and control the cooling amount to keep the LV winding temperature below a predetermined value, or within a safe predetermined operational range. The LV winding temperature may be controlled using a control loop or method similar to that of Figure 6, for example. When the HV winding temperature increases beyond safe operating range the HV control loop may override the LV control loop, or separately control the cooling devices, to increase cooling to ensure that the HV winding temperature is kept within the predetermined operating temperature range. Alternatively, the method may involve selecting which of the HV and LV cooling control methods would provide the higher amount of cooling, and/or power reduction, and operate the fans to provide the higher amount of cooling, and/or control turbine power production to provide the higher amount of power reduction.

All or some of the various method steps described may be implemented in a wind turbine controller, and some of the steps could be implemented in the sensor device itself. For example, sensor output may be an analogue signal that is converted to a temperature value by the control system. Alternatively, if the sensor device has appropriate functionality, the temperature values may be provided directly to the control system.

Fans have been used as an example of cooling devices throughout this document. It will be appreciated that other types of cooling device are compatible with embodiments of the invention. Alternatives such as water cooled, or gas cooled, systems may be used.

DK 2017 70174 A1

Examples have been described in relation to transformers having one or more low voltage coils and one or more high voltage coils. In general, embodiments of the invention are equally applicable to transformers having one or more “medium voltage” (MV) coils, instead of LV coils, and in the description above “LV” could be replaced by “MV”. According to IEC standards, LV coils are coils that operate below 1000V (AC). MV coils are intended to refer to coils that have an operating voltage greater than that of LV coils, but below the corresponding HV coils used in the transformer. This is generally regarded in the field as “medium voltage”. Medium voltage may, in the context of embodiments of the invention, therefore be considered as any operating voltage above that of a LV coil, but below the corresponding HV coil in the transformer. For example, MV coils may be considered to range from 1 kV up to 7.2kV.

For the avoidance of doubt, in any embodiments of the invention an optical temperature sensor may be used as each of the one or more temperature sensors. The optical temperature sensor may be any appropriate touch free or non-contact sensor, such as any of a non-contact thermometer, an infrared camera, an infrared sensor, or a pyrometer.

Many modifications to the embodiments described above are possible and will occur to those skilled in the art without departing from the invention. For example, the controller may be mounted on, and be part of, an individual turbine, or it may be a remote controller which controls multiple turbines which form a wind park or a part of a wind park.

DK 2017 70174 A1

Claims (15)

1. A method of controlling the operating temperature of a wind turbine transformer, the method comprising:

acquiring data indicative of the operating temperature of the wind turbine 5 transformer using at least one remote temperature sensor located at a distance from the transformer and positioned to detect the temperature of at least a portion of the transformer; and operating one or more transformer cooling devices based on the detected temperature to cool the transformer and/or altering the power applied to the transformer

10 based on the detected temperature.

2. A method according claim 1 wherein:

the transformer comprises high voltage coils and low or medium voltage coils, and wherein the at least one temperature sensor is positioned to detect a temperature of the

15 high voltage coils.

3. A method according to claim 2 wherein the at least one temperature sensor is positioned to detect a surface temperature of the high voltage coils.

20

4. A method according to claim 2 or 3 further comprising acquiring data indicative of the operating temperature of the low or medium voltage coils of the transformer using at least one further temperature sensor; and controlling operation of the one or more transformer cooling devices, and/or altering the power applied to the transformer based on the detected temperature, based on the

25 operating temperature of the high voltage and low or medium voltage coils.

DK 2017 70174 A1

5. A method according to claim 4 wherein the one or more transformer cooling devices are operated based upon the detected temperature of the high voltage coils independently to the detected temperature of the low or medium voltage coils.

6. A controller for controlling a wind turbine or a wind power plant, the controller being configured to carry out the method of any of claims 1 to 5.

7. A wind turbine or wind power plant comprising a controller according to claim 6.

8. A wind turbine comprising:

a transformer coupled to the wind turbine generator; and at least one temperature sensor located at a distance from the transformer and positioned to detect the temperature of at least a portion of the transformer, the temperature sensor being coupled to a controller configured to, in use: control the cooling applied to the transformer; and/or to alter the power applied to the transformer based on the detected temperature.

9. A wind turbine according to claim 8 wherein the transformer comprises high voltage coils and low or medium voltage coils, and wherein the at least one temperature sensor is positioned to detect a temperature of the high voltage coils.

10. A wind turbine according to claim 9 wherein the at least one temperature sensor is positioned to detect a surface temperature of the high voltage coils.

11. A wind turbine according to claim 10 wherein the transformer comprises three or more elements corresponding to different phases, with at least one first element arranged

DK 2017 70174 A1 between two other elements, and wherein the at least one temperature sensor is positioned to detect a temperature of the high voltage coil of the first element of the transformer.

12. A wind turbine according to any of claims 9 to 11, comprising at least one further 5 temperature sensor positioned to detect a temperature of the low or medium voltage coils.

13. The method of any of claims 1 to 5, the controller of claim 6, or the wind turbine according to any of claims 7 to 12, wherein the temperature sensor is an optical temperature sensor, and wherein, preferably, the temperature sensor is an infra-red

10 temperature sensor such as a non-contact thermometer, an infrared camera, or a pyrometer.

14. The method of any of claims 1 to 5, the controller of claim 6, or the wind turbine according to any of claims 7 to 13 wherein the temperature sensors are located between

15 200mm and 1000mm from the transformer.

15. A computer program which when executed on a computing device causes it to carry out the method of any of claims 1 to 5.

DK 2017 70174