Patent Publication Number: US-2010111695-A1

Title: Apparatus and method for detecting solid water build-up

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to wind turbines. More specifically, the invention relates to detection of ice and snow on wind turbine blades. 
     Under some conditions, snow and ice can build up on wind turbine blades. The build-up of ice and/or snow on wind turbine blades adversely affects performance of the wind turbine due to the extra weight of the snow and/or ice and alteration of the aerodynamic profiles of the blades. 
     A current technique for ice detection employs an indirect analysis using wind speed as measured by two anemometers, one of which is heated. Another technique compares actual power coefficient and actual power values with expected values. However, these techniques do not detect ice and/or snow in regimes in which such detection is desirable, resulting in a shorter operating season. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An apparatus according to an embodiment comprises a wind turbine with a hub supporting a blade, and a sensor disposed and configured to monitor the blade and to produce a respective output signal. A computer processor disposed and configured to receive the output signal of the sensor executes a computer software application to facilitate comparing the output signal to a predetermined value to determine whether solid water is present at the blade and providing an indication of solid water build-up when solid water is present. 
     According to an embodiment, a system is disclosed comprising a wind turbine comprising a hub supporting a blade and a sensor disposed and configured to monitor the blade and to produce a respective output signal. A computer is disposed and configured to receive data carried by the output signal from the sensor, to compare the data to a predetermined value to determine whether solid water is present at the blade, and to provide an indication of solid water build-up when solid water is present at the blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of an apparatus according to an embodiment of the invention. 
         FIG. 2  is a schematic isometric view of a wind turbine with various example installations according to an embodiment of the invention. 
         FIG. 3  is a schematic flow chart of a method according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the accompanying Figures, examples of a solid water, i.e. snow and ice, build-up monitoring apparatus and method according to embodiments of the invention are disclosed. For purposes of explanation, numerous specific details are shown in the drawings and set forth in the detailed description that follows in order to provide a thorough understanding of embodiments of the invention. It will be apparent, however, that embodiments of the invention may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     A wind turbine blade and solid water, such as snow and ice, have characteristics that can be monitored to determine when solid water build-up is present. The characteristics include, but are not limited to, spectral reflectance, spectral albedo, temperature, and dielectric absorption. For example, the wind turbine blade with no build-up present has reflective characteristics that can serve as reference points or expected values. When build-up forms, the blade with build-up will have different reflective characteristics from the bare surface of the blade. Thus, by comparing the actual reflective characteristics of the vicinity of the blade surface to expected values for the bare surface, build-up can be detected. Additionally, the type and/or thickness of build-up can be determined from variations in the actual values since ice has characteristics that are different from those of snow, and the characteristics of ice and snow will vary with thickness, moisture content, density, and structure of the actual build-up. 
     As seen schematically in  FIG. 1 , a solid water build-up detection apparatus  10  in an embodiment includes an electromagnetic radiation sensor  20  configured to monitor a wind turbine blade. The sensor  20  has a field of view φ expressed, for example, in degrees and produces an output signal  21  indicative of a radiation-related characteristic, such as, but not limited to, reflectivity or reflectance. A computer processor  30 , such as a microprocessor, receives the output signal  21  of the sensor  20 . The computer processor  30  compares the output signal  21  to a predetermined value to determine whether solid water build-up, such as an accumulation of ice and/or snow, is present in the field of view φ. For example, if an infrared sensor is used, then the output signal  21  in an embodiment is indicative of a characteristic of the vicinity of the surface of the blade  105 . In an embodiment, the characteristic is a degree of reflection from the vicinity of the surface of the blade  105  as can be measured, for example, by changes in energy or frequency of radiation received by the sensor from the vicinity of the surface, or by intensity of radiation received. If the reflectance is above a predetermined level or predefined criteria, such as energy or frequency of the reflected ray, then ice and/or snow is present. Since ice and snow have different reflective properties, using more than one predetermined level can distinguish between ice and snow build-up on the blade(s)  105 . In addition snow and/or ice thickness can be determined and a coating of a thickness below a predefined level, such as, for example, from about 0.2 mm to about 3.0 mm, can be ignored/ Alternatively, the output signal in an embodiment is indicative of a surface temperature of the wind turbine blade  105 . If the temperature is below a certain level, then ice and/or snow are likely to be present. 
     The computer processor  30  provides an indication of the presence of solid water build-up when such is present. In an embodiment, the indication is an alarm  31 , such as an audible or visual alarm, and can include an automatic shut down of the wind turbine  100  as well as a notification of the presence of solid water build-up and/or the shut down, such as via e-mail, radio transmission, or other communications methods. In another embodiment, the computer processor  30  is connected to a graphical display  40 , such as a flat panel or CRT display, and the indication takes the form of a graphical representation  41  of the output signal  21  superimposed over an image of the monitored blade(s). Additionally, the computer processor  30  in embodiments enhances the graphical representation  41  of the output signal  21  in areas where solid water build-up is detected. For example, one or more visual cues  42 ,  43 , such as color, can be used to indicate where solid water build-up has been detected. Different cues can be used to indicate the different types of solid water build-up, i.e. ice vs. snow. For example, a first color can be used to indicate ice build-up while a second color can be used to indicate snow build-up. 
     Referring to  FIG. 2 , an example wind turbine  100  includes a support  101 , such as a tower, and a nacelle  102  mounted on the support  101 . The nacelle  102  houses equipment  103 , such as power generation, monitoring, and mechanical transmission equipment. In addition, the nacelle  102  can house the computer processor of embodiments. A hub  104  is supported by the nacelle  102  for rotation relative to the nacelle  102 . At least two wind turbine blades  105  project from the hub  104  and are configured to rotate the hub  104  in response to wind passing over the blades  105 , such as due to the blades  105  having airfoils that generate lift via a pressure difference between a lower pressure surface and a higher pressure surface in a wind. Because of the configuration of the blades  105  and controls over the orientation of the wind turbine, there is a spinward surface (the lower pressure surface) and a spinward direction toward which the blades  105  provide lift when wind passes over the blades  105  in most wind turbines. “Spinward surface” and “spinward direction” can be used even when the blades  105  are not moving since they are configured to move about the axis of rotation in one direction. 
     Various installations of the solid water build-up detection apparatus and method of embodiments are illustrated on the exemplary wind turbine  100  shown in  FIG. 2 . A first example installation  210  in embodiments has at least one electromagnetic radiation sensor  211  configured to be mounted on the hub  104  of the wind turbine  100  adjacent a root of a respective wind turbine blade  105  and to monitor a leading edge of the respective wind turbine blade  105 . One such sensor is provided for each blade in an embodiment, though more or fewer can be provided. 
     A second example installation  220  has at least one electromagnetic radiation sensor  221  configured to be mounted centrally on the nose of the hub  104  of the wind turbine  100  and to monitor one or more respective wind turbine blade  105 . In an embodiment, the sensor  221  monitors just one blade  105 , but in other embodiments, the sensor  221  monitors all blades of the wind turbine, such as by scanning each blade one at a time. In other embodiments, multiple sensors  221  can be mounted at the nose of the hub  104  so that all blades  105  can be monitored simultaneously. 
     A third example installation  230  has at least two electromagnetic radiation sensors  231 ,  232  for each blade  105 . Each sensor  231 ,  232  is configured to monitor a respective main wind direction of the wind turbine blade  105  they monitor and are mounted proximate to a hub  104  of the wind turbine  100 . In an embodiment, one of the sensors  231  monitors a leading edge of the wind turbine blade  105 , and another of the sensors  232  monitors a lower pressure surface, such as a spinward surface, of the wind turbine blade  105 . 
     A fourth example installation  240  has an electromagnetic radiation sensor  241  configured to be mounted on a nacelle  102  of the wind turbine  100  and monitors surfaces of the wind turbine blades  105  in a windward field of view. Multiple sensors  241  are used in embodiments, though a single sensor  241  can be used to monitor all of the blades  105 . 
     As mentioned above, an embodiment of the invention includes computer-implemented processes or methods and apparatus for practicing such processes, such as the computer processor  30 . Additionally, as also mentioned above, an embodiment includes a computer software application or program product that includes computer code, such as object code, source code, or executable code, on tangible media, such as magnetic media (floppy diskettes, hard disc drives, tape, etc.), optical media (compact discs, digital versatile/video discs, magneto-optical discs, etc.), random access memory (RAM), read only memory (ROM), flash ROM, erasable programmable read only memory (EPROM), or any other computer readable storage medium on which the computer program code is stored and with which the computer program code can be loaded into and executed by a computer. When the computer executes the computer program code, it becomes an apparatus for practicing the invention, and on a general purpose microprocessor, specific logic circuits are created by configuration of the microprocessor with computer code segments. A technical effect of the executable instructions is to monitor wind turbine blades for build-up of solid water, such as ice and snow, and to provide an indication of such build-up when detected, such as by triggering an alarm or displaying a graphical representation of the areas in which the build-up has been detected. The graphical representation in an embodiment uses cues, such as color, to emphasize the areas of build-up. Additionally, the graphical representation in an embodiment is superimposed on an image of a respective wind turbine blade. 
     The computer program code is written in computer instructions executable by the computer processor, such as in the form of software encoded in any programming language. Examples of suitable programming languages include, but are not limited to, assembly language, VHDL (Verilog Hardware Description Language), Very High Speed IC Hardware Description Language (VHSIC HDL), FORTRAN (Formula Translation), C, C++, C#, Java, ALGOL (Algorithmic Language), BASIC (Beginner All-Purpose Symbolic Instruction Code), APL (A Programming Language), ActiveX, HTML (HyperText Markup Language), XML (eXtensible Markup Language), and any combination or derivative of one or more of these. 
     The computer program or software application executes a method  300  schematically illustrated in  FIG. 3  in which the output signal(s)  21  of the sensor(s)  20  is (are) received (block  310 ) and compared to a predetermined value (block  320 ). If the comparison is not indicative of build-up, then new values of the sensor output signal(s) are received for comparison at block  320  to continue monitoring. If the comparison is indicative of build-up, then an indication of build-up is provided (block  330 ) such as by triggering an alarm (block  340 ) or by providing a graphical representation  41  (block  350 ). In addition, one or more cues  42 ,  43  can be provided to emphasize areas of build-up (block  360 ). New values of the sensor output signal(s) are received for comparison at block  320  to continue monitoring. 
     By using the apparatus and/or system implementing the method according to embodiments, solid water build-up can be detected to prevent damage to, enhance efficiency of, and/or prevent injury to personnel working on wind turbines. Additionally, by enabling detection of ice and snow build-up, the operational season of wind turbines can be extended in areas in which conditions induce such build-up. 
     While the instant disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope thereof In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.