WIND TURBINE WITH AN OPTICAL SENSOR

Description

[0001] The invention relates to a wind turbine with an optical sensor and a method for operating such a wind turbine.

[0002] Wind turbines are generally exposed to environmental influences and weather conditions. During operation, water and, at low temperatures, ice can adhere to the rotor blades. This affects and potentially reduces the turbine's performance. In extreme cases, damage can occur.

[0003] When a layer of ice forms on the rotor blades of a wind turbine, this ice can break off, for example, due to a rise in temperature, and strike the ground within a specific area below the turbine. This is known as ice breakage. Such an ice breakage poses a significant danger to people and objects located within this area. Therefore, it is standard practice to shut down wind turbines in a timely manner when there is a risk of ice formation.

[0004] Systems are known that use two sensors to protect wind turbines. One sensor detects whether icing is present on the rotor blades, while another monitors the fall zone or danger zone below the turbine for people and / or objects. A control system shuts down the turbine if both icing is present and a person or object is within the monitored danger zone. Furthermore, optical systems are known that use multiple wavelengths in the infrared range to detect ice.

[0005] One disadvantage of known systems is that multiple sensors are required to monitor a wind turbine for both ice on the rotor blades and for people or objects below the turbine. Furthermore, it can be difficult for known systems to reliably assess a detected ice layer on a wind turbine rotor blade, for example, regarding the thickness of the ice layer.

[0006] From WO 2013 / 149811 A1, a wind turbine and a method with the features according to the respective preamble of the independent claims are known.

[0007] US patent 2014 / 0363293 A1 describes a wind turbine and process with features according to a related technology.

[0008] One object of the invention is to create a wind turbine with an optical sensor that is able to simultaneously monitor rotor blades of a wind turbine with regard to a predetermined foreign material such as ice and a predefined area below the wind turbine with regard to objects and persons.

[0009] This problem is solved by a wind turbine and by a method with the features of the respective independent claims. Advantageous embodiments of the invention are specified in the dependent claims, the description, and the drawings.

[0010] The wind turbine comprises a rotor with multiple rotor blades and an optical sensor. The optical sensor includes a light source that emits light into a predetermined monitoring area and a receiving and evaluation unit configured to detect at least one object within the monitoring area based on received light emitted by the light source and remitted (in particular, reflected) by the object. The light source is further configured to emit light at at least two different wavelengths, while the receiving and evaluation unit is additionally configured to determine the respective intensity of the light remitted by the object for each of the at least two wavelengths and, based on the ratio of at least two intensities at different wavelengths, to detect at least one predetermined material on the object.

[0011] The optical sensor is mounted on the wind turbine in such a way that its monitoring area covers a predetermined protective zone below the rotor, at least temporarily. During operation, at least one of the multiple rotor blades is also within the sensor's monitoring area, at least temporarily. This enables the sensor to detect at least one predetermined material on at least one of the multiple rotor blades. Therefore, the wind turbine requires only a single optical sensor to simultaneously monitor the predetermined area or protective zone below the rotor and detect a predetermined material, such as water and / or ice, on at least one of the rotor blades. This reduces the complexity of the sensor system required for the safe operation of the wind turbine.

[0012] The at least one object thus includes both people and objects such as vehicles within the predetermined protection zone below the wind turbine, as well as the rotor blade of the wind turbine itself. The monitoring area can, for example, permanently cover the predefined protection zone below the wind turbine, and a rotor blade of the wind turbine can also move through the sensor's monitoring area during operation.

[0013] The optical sensor thus has a dual function, as it can both detect the presence of objects within the monitored area and identify one or more materials on such an object, which could be, for example, foreign materials or foreign bodies. Such foreign materials include, in particular, water or ice, which might be found, for instance, on a wind turbine rotor blade within the monitored area.

[0014] Since the light source emits at least two different wavelengths and the reflection or remission of the emitted light at these different wavelengths is evaluated accordingly, only a single optical sensor is required for detecting objects within the monitored area on the one hand, and for detecting at least one predetermined material, especially foreign material, on such objects on the other. This reduces the costs for the necessary sensor technology, particularly during the operation of a wind turbine.

[0015] Since at least one material is predetermined, which is in particular water and / or ice, the at least two wavelengths can be determined based on the material's properties. This is done by determining the at least one predetermined material based on the ratio of the at least two light intensities detected due to the reflection or remission of light at these wavelengths.

[0016] The sensor can be configured for time-of-flight measurement within a predetermined spatial region surrounding the optical sensor. For example, the sensor can include a laser scanner that allows three-dimensional scanning of the monitored area and can be specifically designed for distance measurement. Furthermore, for each point in three-dimensional space where an object is detectable, the optical sensor can detect the presence of the predetermined material.

[0017] The optical sensor can also be a frequency-modulated continuous wave (FMCW) system. For example, an FMCW LiDAR system can enable distance measurement between the object and the sensor with high spatial resolution. Furthermore, such systems offer long ranges with minimal interference. In addition, optical FMCW systems can operate in a near-infrared wavelength range, for example, between 1300 nm and 1800 nm, in which the ratio of light reflectance changes depending on the wavelength, for example, for water and ice, thus enabling the detection of these materials based on their intensity ratios.

[0018] According to one embodiment, the light source of the optical sensor emits light at at least two discrete, predetermined wavelengths, while the receiving and evaluation unit is further configured to detect light in a wavelength range encompassing the at least two discrete wavelengths of the light source. In other words, the receiving and evaluation unit can be configured to receive and evaluate light in a broadband wavelength range that includes the at least two discrete wavelengths at which the light source emits light. The receiving and evaluation unit can thus include an optically broadband detector for which no special technical requirements exist and which can therefore be designed cost-effectively.

[0019] Alternatively, the light source can emit light in a predetermined broad wavelength range, while the receiving and evaluation unit can further be configured to detect light at least two discrete, predetermined wavelengths that lie within the wavelength range of the light source. In this embodiment, the receiving and evaluation unit comprises a narrowband and, for example, tunable detector, which, for example, has filters that are only transparent in a narrow range around the at least two predetermined wavelengths, while broadband illumination with respect to wavelength is provided by the light source. Thus, in this embodiment, the requirements for the light source are minimal, while the determination of the at least two discrete, predetermined wavelengths for detecting the predetermined material on an object is carried out within the receiving and evaluation unit.

[0020] Furthermore, the at least two discrete, predetermined wavelengths can be selected such that the receiving and evaluation unit is able to detect at least two types of the predetermined material or two predetermined materials on the object based on the ratio of the at least two intensities at the at least two wavelengths. For example, the reflection of light at the at least two discrete, predetermined wavelengths can differ for the different types of material or different materials, such as water and ice.

[0021] The sensor can therefore be designed to detect the light reflectance of water and ice as the different types of material. As mentioned above, the ratio of light reflectance for water and ice changes in the near-infrared range, for example between 1300 and 1800 nm, so that the ratio of two light intensities within this wavelength range allows the detection of water and ice on an object.

[0022] According to a further embodiment, the receiving and evaluation unit can also be configured to classify an object when the object is detected within the sensor's monitoring range. In other words, a detected object can be assigned to one of several object classes.

[0023] Such object classes can include, for example, an object class for people, an object class for vehicles, and further object classes for other objects. If the optical sensor is designed for time-of-flight measurement in a predetermined spatial area—for example, as a suitably configured laser scanner, a TOF camera (Time Of Flight), or an FMCW LiDAR system—the three-dimensional acquisition of object points enables, for example, an assignment to known object patterns in the sense of object recognition, which can be carried out by means of the receiver and evaluation unit. Based on the recognition of a predetermined contour and / or dimensions of an object within a predetermined area, an object can be assigned to a specific object class. For example, with an object length of 5 m, it is very likely that the object is a vehicle and not a person.

[0024] According to another embodiment, the optical sensor comprises an optical scanner, in particular a laser scanner.

[0025] According to another embodiment of the wind turbine, the optical sensor is attached to a static element of the wind turbine. The sensor can be mounted, for example, in the area of ​​a rotor's axis of rotation, such as on a bracket near its bearing. The sensor can be oriented such that its monitoring area below the wind turbine's rotor covers a predetermined area on the ground beneath the turbine.

[0026] In this embodiment, it is additionally required that the optical sensor at least partially "sees" one rotor blade of the wind turbine, i.e., that the rotor blade is located within the monitoring range of the optical sensor for a predetermined period and, for example, traverses it. If the time required for a rotor blade to traverse the monitoring range is recorded, and the dimensions of the monitoring range are known, a so-called "traverse speed" of the rotor blade through the monitoring range can be determined based on this time, which in turn allows the determination of the rotational speed of the wind turbine rotor.

[0027] Alternatively, the optical sensor can be mounted on one of the rotor blades. In one embodiment, the optical sensor can be mounted on the inner end of one of the rotor blades. This inner end can be located near the rotor's axis of rotation, so that the sensor's monitoring area permanently encompasses, for example, almost one side of a rotor blade. Since the optical sensor rotates with the rotor blade to which it is mounted in this embodiment, the optical sensor, or rather its monitoring area, sweeps across a predetermined protective field on the ground beneath the wind turbine within a specific timeframe during the rotor's rotation. This protective field can be defined by the optical sensor's range, which determines the boundary or maximum distance of an object within the monitoring area.

[0028] The predetermined protective field below the wind turbine rotor can thus be defined by superimposing the sensor's monitoring area during its rotation, together with the rotor blade, and a plane in the ground area below the wind turbine. In other words, the protective field can be defined by ensuring that the optical sensor's field of view, which determines its monitoring area, sweeps over a specific area on the ground as the sensor rotates with the rotor.

[0029] In an alternative embodiment, the optical sensor is mounted at the outer end of one of the multiple rotor blades. The outer end of the rotor blade is located at its tip, which is furthest from the rotor's axis of rotation. In this embodiment, however, it is necessary that at least part of the rotor blade be visible to the sensor, even though it is mounted at the outer end of that blade, and that the sensor be oriented such that it can monitor a predetermined protective field below the rotor for a predetermined period. Mounting the optical sensor at the outer end of the rotor blade has the advantage that a short range of the optical sensor is required due to the relatively short distance to the ground when the rotor blade is in its lowest position above the ground.The range of the optical sensor can therefore be less in this embodiment than in the embodiment in which the optical sensor is attached to an inner end of one of the several rotor blades.

[0030] The sensor can further be designed to detect the reflection of light by water and ice. In this embodiment, the at least two wavelengths at which the optical sensor can emit or detect light are selected such that the reflection of light by water and ice differs at these predetermined wavelengths. This allows water and ice to be detected based on the intensity ratio at these selected wavelengths.

[0031] The optical sensor can also be configured to determine the thickness of an ice layer on one of the rotor blades, taking a reference measurement into account. This reference measurement can be taken, for example, under conditions where it is ensured that no ice is present on any of the wind turbine's rotor blades. Depending on the ice layer thickness, the optical sensor can also issue a warning signal that can be considered during wind turbine operation. Alternatively, monitoring of the area beneath the wind turbine for the presence of objects can be activated only when the ice layer thickness on one of the rotor blades exceeds a predetermined value. For example, during a reference measurement without ice, the sensor measures the distances to the rotor blade and then has a reference value against which it can measure the current ice layer thickness.

[0032] Each optical sensor, as described above, can be provided on several, preferably all, rotor blades of the wind turbine. Using multiple optical sensors on individual rotor blades improves the reliability with which the at least one predetermined material, in particular ice, can be detected on the rotor blades. Furthermore, the predetermined area beneath the wind turbine can be monitored more reliably than when using a single optical sensor on only one rotor blade, since the predetermined area is scanned more frequently or at a higher frequency by the optical sensors. Conversely, the time interval during which no sensor covers or scans the predetermined area is shorter when using multiple sensors on individual rotor blades than when using a single sensor on only one rotor blade.

[0033] A further object of the invention is a method for operating a wind turbine as described above. The method comprises using an optical sensor to monitor, on the one hand, a predetermined protective field below the rotor of the wind turbine for the presence of at least one object, and on the other hand, to monitor at least one of the rotor blades of the wind turbine for the presence of a predetermined material, in particular ice.

[0034] The method is therefore intended for the operation of the wind turbine described above. Consequently, the explanations regarding the wind turbine apply accordingly to the method, particularly with regard to advantages and preferred embodiments. Furthermore, it is understood that all features mentioned herein are combinable unless explicitly stated otherwise.

[0035] The method again utilizes the dual function of the optical sensor described above, whereby it simultaneously monitors the predetermined protective field below the wind turbine rotor for objects and monitors or detects a predetermined material on one of the rotor blades. The predetermined protective field can either be permanently covered by the sensor's monitoring area if it is installed on a static element of the wind turbine, or it can be defined by the optical sensor's monitoring area sweeping a specific area below the wind turbine rotor for a predetermined period. The predetermined protective field is thus defined by the optical sensor's monitoring area and by the specific way the sensor is installed on the wind turbine.

[0036] According to one embodiment of the method, the monitoring of the protective field below the rotor of the wind turbine with regard to the presence of at least one object is only carried out or activated when the predetermined material, in particular ice, is present.

[0037] According to a further embodiment of the method, if both the predetermined material, which is in particular ice, is present on the at least one rotor blade and if at least one object is present in the protective field, it is determined whether the wind turbine should be shut down. According to this embodiment, the wind turbine can therefore be shut down if two conditions are met: namely, if the predetermined material, such as ice, is detected on the rotor blade and simultaneously an object is located within the protective field.

[0038] The wind turbine can also be shut down upon detection of ice, provided other conditions are met. For example, the thickness of an ice layer can be measured to shut down the wind turbine if this thickness exceeds a predetermined value. Furthermore, objects within the sensor's monitoring area or protective field can be classified, and the wind turbine can then be shut down if a specific type of object, such as a person, is within the protective field.

[0039] Furthermore, signals from other sensors, such as those for humidity, air pressure, and air temperature, can be considered when deciding whether to shut down the wind turbine. Additionally, the system can issue a warning based on the thickness of any ice layer on one of the rotor blades. For example, if the environmental conditions around the wind turbine—that is, the humidity, air pressure, and air temperature—indicate a low probability of ice breaking off the rotor blades, and if, at the same time, a low mass or thickness of ice is detected on one of the rotor blades, the wind turbine can continue operating even if only a vehicle, but no person, is within the protected area.However, if a person is detected within the protective field under the same environmental conditions, the wind turbine should be switched off, as even small pieces of ice falling from the rotor blades of the wind turbine can cause significant injuries to a person.

[0040] Furthermore, if, according to one embodiment, both the thickness of an ice layer on one of the wind turbine's rotor blades and the rotational speed of the wind turbine's rotor are determined—the latter, for example, based on the "crossing speed" of the rotor through the sensor's monitoring area described above—the size of the protective field below the rotor can be adjusted based on the rotational speed and the thickness of the ice layer. For example, the protective field can be smaller at a low rotational speed and / or a small or negligible ice layer thickness than at a high rotor rotational speed or a significant ice layer thickness.

[0041] The invention is described below by way of example with reference to an advantageous embodiment and the accompanying figures. These show, schematically: Fig. 1 an optical sensor, Fig. 2 a wind turbine according to the invention with the sensor of Fig. 1 and Figs. 3A and 3B two embodiments in which the optical sensor of Fig. 1 each is attached to a rotor blade of a wind turbine in a different way.

[0042] Fig. 1 Figure 1 shows a schematic representation of an optical sensor 100, which includes a light source 110 and a receiver and evaluation unit 120. The receiver and evaluation unit 120 in turn comprises a receiver section 122, which is configured to detect incident light and convert it into a corresponding electrical signal, and an evaluation section 124. The evaluation section 124 is designed to output a control signal 126 for controlling the light source 110. Furthermore, the evaluation section 124 outputs a signal 128 from the optical sensor 100.

[0043] The light source 110 emits light in the form of a laser beam 130 into the vicinity of the optical sensor 100. The emitted light can be remitted or reflected by an object 140, so that a remitted or reflected portion of the laser beam 130 emitted by the light source 110 reaches the receiver 122 of the receiver and evaluation unit 120 as received light 142.

[0044] The optical sensor 100 is further assigned a predetermined monitoring area 150, the boundaries 152 of which are schematically indicated by dashed lines. The light source 110 emits light into the predetermined monitoring area 150 by changing the direction of the laser beam 130, as indicated by the arrow 154. Due to the deflection of the laser beam 130, it sweeps across the predetermined monitoring area 150, from which the receiver 122 receives the emitted or reflected light 142. The monitoring area 150 is thus defined by the spatial region in which the light source 110 emits the laser beam 130 and from which, simultaneously, the receiver 122 of the receiving and evaluation unit 120 can receive the emitted or reflected light 142.The predetermined monitoring area 150 is limited in the direction of view of the optical sensor 100 by the range of the light source 110, as schematically indicated by the arrow 156.

[0045] The optical sensor 100 is designed to detect, by means of the receiving and evaluation unit 120, objects, such as object 140, within the monitoring area 150, based on the received light 142, that is emitted by the light source 110 and remitted or reflected by object 140. Furthermore, the light source 110 is designed to emit light or a laser beam 130 at at least two different wavelengths. The receiving and evaluation unit 120 is accordingly designed to determine the intensity of the remitted or reflected light 142 for each of the at least two wavelengths. Based on the ratio of at least two intensities of the remitted or reflected light at the at least two different wavelengths, the receiving and evaluation unit 120 can detect at least one predetermined material or foreign material 160 on object 140.

[0046] To detect the presence of at least one material or foreign material 160 on the object 140, the at least two wavelengths at which the light source 110 emits light in the form of the laser beam 130 are selected such that the remission or reflection of light at the foreign material 160, whose detection is desired, differs. The material 160 then exhibits a known remission ratio at the at least two wavelengths.

[0047] If the foreign material 160, which may be detected by the sensor, is, for example, ice—that is, if an ice layer on the object 140 is to be detected—wavelengths in the near-infrared between 1300 nm and 1800 nm are suitable for detecting ice, since the reflectance ratio between, for example, water and ice changes depending on the wavelength in this wavelength range. Based on the evaluation of the intensity differences, which are determined by the receiving and evaluation unit 120 at the at least two wavelengths, the optical sensor 100 can not only detect the presence of an object 140 within the monitoring area 150 and determine its spatial location, but also detect the foreign material 160, for example, ice, on the object 140.

[0048] The optical sensor 100 operates on the principle of a laser scanner. Furthermore, the optical sensor 100 can be configured, for example, as a TOF camera (Time Of Flight), in which time-of-flight measurements are performed, or as a frequency-modulated continuous wave LiDAR system (FMCW LiDAR system, FMCW being Frequency Modulated Continuous Wave). Such variants of the optical sensor 100 allow for distance measurement within a predetermined three-dimensional spatial area, i.e., within the monitoring area 150 of the optical sensor 100.

[0049] Furthermore, by comparison with a reference measurement, it is possible to determine the thickness of the foreign material 160 on the object 140, for example, the thickness of an ice layer. The reference measurement is performed under conditions in which it is ensured that no foreign material 160 is present on the object 140. If it is also known that the object 140 is in the same position when the foreign material 160 is present as it was during the reference measurement, the thickness of the foreign material 160 can be determined by a measurement using a TOF camera or an FMCW LiDAR system. This is achieved by determining the spatial or three-dimensional position of the surface of the foreign material 160 facing the optical sensor 100.Since the reference measurement provides the spatial location of the corresponding surface of object 140 without the foreign material 160, the thickness of the foreign material 160 on object 140 can be determined by comparing the two measurements.

[0050] In Fig. 2 A schematic representation of a wind turbine 200 is shown, to which an optical sensor 100 is attached, as described above. The wind turbine 200 comprises a rotor 210 with rotor blades 212, which are attached to a rotor shaft 214 for rotation.

[0051] The optical sensor 100 operates on the principle of a laser scanner. It scans the monitoring area 150, for example, by periodically deflecting the laser beam 130 emitted by the light source 110. The monitoring area 150 of the optical sensor 100 is thus defined by controlling the deflection of the laser beam 130 so that it covers the desired monitoring area 150.

[0052] The optical sensor 100 is mounted on a bracket 216 as part of the wind turbine 200, which is designed such that the optical sensor 100, or the monitoring area 150 associated with the optical sensor 100, is always oriented in the same downward direction towards the ground below the wind turbine 200 or the rotor 210. During operation of the wind turbine 200 with the rotor 210 rotating, the optical sensor 100 therefore rotates in the embodiment of Fig. 2 not with the rotor 210, so that the monitoring area 150 of the sensor 100 is to be considered stationary and a protective field 220 is defined below the rotor 210 of the wind turbine 200.

[0053] As in connection with Fig. 1 As described, the sensor 100 is designed to detect objects 140 within the monitoring area 150 or the protective field 220 below the rotor 210. Fig. 2 A person 230 and a vehicle 232 are shown as examples of objects 140 located on the ground below the wind turbine 200 within the protected area 220. Furthermore, the rotor blades 212 also represent objects 140 that are visible or detectable by the sensor 100 as soon as one of the rotor blades 212 is located within the monitoring area 150 during rotation of the rotor 210. During the rotation of the rotor 210, the respective rotor blade 212 thus traverses the monitoring area 150 of the sensor 100 for a specific period of time, which is determined by the rotational speed of the rotor 210. During this period, an area or section 240 of the respective rotor blade 212 is located within the monitoring area 150 of the sensor 100.

[0054] Since the sensor 100 emits at least two wavelengths in the range between 1300 nm and 1800 nm, the sensor 100 is able not only to detect the presence of the rotor blade 212 within the monitoring area 150, but also the presence and thickness of a layer of foreign material 160 (cf. Fig. 1 ) such as ice on the rotor blade 212. The optical sensor 100 can therefore detect an ice layer on the rotor blade 212 in addition to the presence of objects 140 within the monitoring area.

[0055] As explained above, the optical sensor 100 can also determine the thickness of such an ice layer on the rotor blade 212 using a reference measurement. For this purpose, a reference measurement is taken under conditions that ensure there is no ice layer on the rotor blades 212. Such conditions can be defined, for example, based on humidity, air temperature, and air pressure, if these parameters are measured using additional sensors.

[0056] The monitoring of the protective field 220 below the rotor 210 of the wind turbine 200 for the presence of at least one object 140 can, for example, only be activated if the foreign material 160, which is primarily ice, is detected on at least one of the rotor blades 212. Furthermore, even if ice is detected on one of the rotor blades 212, the monitoring of the protective field 220 can, for example, only be activated if the thickness of the ice layer exceeds a predetermined value.

[0057] Furthermore, the time during which one of the rotor blades 212 passes through the monitoring area 150 of the sensor 100 and is thus visible to the optical sensor 100 can be measured. If the dimensions of the monitoring area 150 of the optical sensor 100 are known, a so-called "passage speed" of the rotor blade 212 through the monitoring area 150 and consequently the rotational speed of the rotor 210 can be determined.

[0058] The size of the protective field 220 can be adjusted based on the determined rotational speed of the rotor 210 and the thickness of the foreign material 160 or the ice layer on the rotor blades 212. For example, a larger protective field 220 can be set at a high rotational speed of the rotor 210 than at low rotational speeds of the rotor 210. Likewise, the protective field 220 can be increased if a certain thickness of the ice layer on one of the rotor blades 212 is exceeded. The size of the protective field 220 is adjusted by changing the spatial area covered by the laser beam 130 (see figure). Fig. 1 ) scans.

[0059] If the optical sensor 100 is configured as a TOF camera or as an FMCW LiDAR system, it can perform three-dimensional scanning of objects 140 within the monitoring area 150. Based on the three-dimensional measurement points of the optical sensor 100, which can be assigned to the respective objects 140, the optical sensor 100 is also able to classify the objects 140. The detected objects 140 can thus be assigned to specific object classes based on predefined contours or predefined areas for their dimensions, for example, to the object class "person" or the object class "vehicle". In other words, the optical sensor 100 is designed to distinguish, for example, between a person 230 and a vehicle 232 among the detected objects 140 and to assign them to the corresponding object classes.

[0060] Furthermore, the operation of the wind turbine 200 is controlled depending on the presence and thickness of the ice layer on the rotor blades 212. If icing of the rotor blades 212 is detected and the thickness of the ice layer exceeds a predetermined value, the wind turbine 200 can be shut down to prevent endangering persons 230 and other objects 140 within the safety zone 220 due to an ice break. In such an ice break, the ice layer or mass breaks away from the rotor blades 212, causing pieces of ice to fall to the ground within the safety zone 220 and thus pose a danger to persons 230 and other objects 140 within the safety zone 220.

[0061] However, if only a small mass of ice or a thin layer of ice is detected on the rotor blades 212 and no persons 230 are within the protective zone 220, the wind turbine 200 can continue to operate, even if, for example, a vehicle 232 is within the protective zone 220. In such a case, no or only minor damage from falling pieces of ice can be expected. However, if a person 230 is detected within the protective zone 220, the wind turbine 220 will be shut down even with a thin layer of ice, as even small pieces of ice pose a danger to the person 230 if they fall. The decision regarding continued operation of the wind turbine 200 therefore depends, if necessary, on the thickness of the detected ice layer or mass and on the classification of the objects 140 within the protective zone 220.

[0062] In Fig. 3 Alternative embodiments for mounting the optical sensor 100 on the wind turbine 200 are shown schematically. In the two embodiments of Fig. 3A und 3B The optical sensor 100 is attached to one of the rotor blades 212, so that the optical sensor 100 rotates together with the rotor 210 around its axis of rotation 215 during the operation of the wind turbine 200.

[0063] The Fig. 3A und 3B These are to be understood as perspective views of the rotor blade area. In each illustration, the axis of rotation 215 points obliquely from the right behind the plane of the figure to the left in front of the plane of the figure. The optical sensor 100 is designed as a scanner, with its scan plane extending obliquely to the left and forward in the same direction as the axis of rotation 215. The scan direction is indicated by the double arrow 222. The dashed lines 223 in the Fig. 3A und 3B are therefore each directed obliquely forwards from the plane of the figure, while the dashed line 224 in the Fig. 3B is directed obliquely backwards. The dashed lines 223 and 224 lie in the respective scan plane of the optical sensor 100, which is designed as a scanner and rotates around the axis of rotation 215 together with the rotor blade 212 when the rotor 210 rotates.

[0064] By arranging the optical sensor 100, designed as a scanner, on the rotating rotor blade 212, the scan plane rotates in the arrangements of the Fig. 3A und B with the rotor 210. The rotor rotation therefore automatically causes the protective field below the rotor blade 212 to be swept over, in contrast to the arrangement of the Fig. 2 with fixed sensor 100. There, an additional swiveling of the scan plane must be implemented to cover the monitoring area 150 and thus the protective field 220.

[0065] In the embodiment of Fig. 3A The optical sensor 100 is attached to an inner end of the rotor blade 212 near the rotor shaft 214 or near the axis of rotation 215 of the rotor 210. The monitoring area 150 of the optical sensor 150 therefore encompasses an outer surface of the rotor blade 212 to which the optical sensor 100 is attached. The rear surface of the rotor cannot be detected here, unless, for example, another sensor is provided there. As the rotor 210 rotates, the monitoring area 150 of the optical sensor 100 periodically scans the ground beneath the wind turbine 200 for a predetermined duration. The protective field 220 (see...) Fig. 2 ) below the rotor 210 is thus defined in this embodiment by the range of the optical sensor 100 during the periodic scanning of the ground by the monitoring area 150.

[0066] In the embodiment of Fig. 3B In contrast, the optical sensor 100 is attached to an outer end of the rotor blade 212. This outer end of the rotor blade 212 is located at the tip of the rotor blade 212, which is furthest away from the rotor shaft 214 or the axis of rotation 215. This also applies to the embodiment of Fig. 3B At least a part or section of the rotor blade 212 is visible to the optical sensor 100 in order to be able to carry out the monitoring of the rotor blade 212 with regard to ice as described above, as illustrated by the dashed lines.

[0067] In the embodiment of Fig. 3B The optical sensor 100, or rather its monitoring area 150, is additionally oriented towards the ground, i.e., away from the rotor blade 212, so that the monitoring area 150 of the optical sensor 100 is the same as in the embodiment of Fig. 3A The ground beneath the rotor 210 is periodically swept, thereby defining the protective field 220. The embodiment of Fig. 3B This has the advantage that the optical sensor has a shorter range of 100 than in the embodiment of Fig. 3A This is necessary because the optical sensor 100 is located closer to the ground during the operation of the wind turbine 200 when the monitoring area 150 of the optical sensor 100 covers the ground. Furthermore, with a corresponding arrangement or a correspondingly extended scan plane (for example, to the back of the rotor blade), objects on the back of the rotor blade 212 are also detectable in the embodiment of Fig. 3B due to the placement of the optical sensor 100 at the tip of the rotor blade 212, it is visible to this, whereas such objects are not visible to the embodiment of Fig. 3A (if only one sensor is present) are not visible. Bezugszeichenliste

[0068] 100 Optical sensor 110 Light source 120 Receiver and evaluation unit 122 Receiver section 124 Evaluation section 126 Control signal 128 Output signal 130 Emitted light or laser beam 140 Object 142 Remitted or reflected light 150 Monitoring area 152 Boundary of the monitoring area 154 Displacement of the laser beam 156 Range of the optical sensor 200 Wind turbine 210 Rotor 212 Rotor blade 214 Rotor shaft 215 Axis of rotation 216 Mounting bracket for the optical sensor 220 Protective field 222 Scan direction 223, 224 Dashed lines to illustrate the orientation of the scan plane 230 Person 232 Vehicle 240 Area on the rotor blade visible to the optical sensor

Claims

1. A wind turbine (200) comprising: a rotor (210) having a plurality of rotor blades (212); an optical sensor (100) which comprises: a light source (110) which emits light (130) into a predetermined monitored zone (150), and a receiving and evaluating unit (120) which is configured to detect at least one object (140) within the monitored zone (150) based on received light (142) which is emitted by the light source (110) and remitted by the object (140), wherein the light source (110) is further configured to emit light at at least two different wavelengths, and wherein the receiving and evaluating unit (120) is further configured to determine a respective intensity of the light (142) remitted by the object (140) for a respective one of the at least two wavelengths and to detect at least one predetermined material (160) at the object (140) based on a ratio of at least two intensities at different wavelengths, wherein, during the operation of the wind turbine (200), at least one of the plurality of rotor blades (212) is located at least temporarily in the monitored zone (150) of the sensor (100) and the sensor (100) is thereby able to detect the at least one predetermined material (160) at the at least one of the plurality of rotor blades (212), characterized in that the optical sensor (100) is attached to the wind turbine (200) such that the monitored zone (150) at least temporarily covers a predetermined protected field (220) below the rotor (210).

2. A wind turbine (200) according to claim 1, wherein the light source (110) of the optical sensor (100) emits the light (130) at at least two discrete, predetermined wavelengths, and the receiving and evaluating unit (120) is further configured to detect light (142) in a wavelength range which comprises the at least two discrete wavelengths of the light source (110), or the light source (110) emits the light (130) in a wavelength range and the receiving and evaluating unit (120) is further configured to detect light (142) at at least two discrete, predetermined wavelengths which lie within the wavelength range of the light source (110).

3. A wind turbine (200) according to claim 2, wherein the at least two discrete predetermined wavelengths are selected such that the receiving and evaluating unit (120) is capable of detecting at least two types of the predetermined material (160) at the object (140) based on the ratio of the at least two intensities at the at least two wavelengths.

4. A wind turbine (200) according to claim 3, wherein the sensor (100) is designed such that it is capable of detecting the remission of light with water and ice as the different types of the material (160).

5. A wind turbine (200) according to any one of the claims 1 to 4, wherein the receiving and evaluating unit (120) is further configured to classify an object (140) if the object (140) can be detected in the monitored zone (150) of the sensor (100).

6. A wind turbine (200) according to any one of the claims 1 to 5, wherein the optical sensor (100) comprises an optical scanner, preferably a laser scanner which is in particular configured for distance measurement.

7. A wind turbine (200) according to any one of the claims 1 to 6, wherein the optical sensor (100) is attached to a static element (214) of the wind turbine (200).

8. A wind turbine (200) according to any one of the claims 1 to 6, wherein the optical sensor (100) is attached to one of the plurality of rotor blades (212).

9. A wind turbine (200) according to claim 8, wherein the optical sensor (100) is attached to an inner end of one of the plurality of rotor blades (212).

10. A wind turbine (200) according to claim 8, wherein the optical sensor (100) is attached to an outer end of one of the plurality of rotor blades (212).

11. A wind turbine (200) according to any one of the claims 1 to 10, wherein the optical sensor (100) is designed such that it is capable of detecting the remission of light for water and / or ice, wherein the optical sensor (100) is preferably further configured such that it is capable of determining a thickness of an ice layer at one of the plurality of rotor blades (212) taking into account a reference measurement.

12. A wind turbine (200) according to any one of the claims 1 to 10, wherein an optical sensor (100) is provided at a plurality of rotor blades (212), preferably at all the rotor blades.

13. A method of operating a wind turbine (200) according to any one of the claims 1 to 12, wherein the method comprises that by means of the optical sensor (100): at least one of the rotor blades (212) of the rotor (210) of the wind turbine (200) is monitored with respect to the presence of a predetermined material (160), in particular ice, characterized in that a predetermined protected field (220) below the rotor (210) of the wind turbine (200) is monitored with respect to the presence of at least one object (140).

14. A method according to claim 13, wherein, if both the predetermined material (160), in particular ice, is present at the at least one rotor blade (212) and the at least one object (140) is present in the protected field (220), it is determined whether the wind turbine (200) is to be switched off.