design of ice-free anemometers |
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The Ice-Free Anemometer development project is being led by Prof. Jean Ruel and co-supervised by Prof. Jean Lemay at Université Laval. Three graduate students have been involved in the project and one of them, the Ph.D. candidate André Bégin-Drolet, is currently working on it. The project has advanced to a third generation prototype (see Fig. 1) of the technology and is under field test at the Wind Energy Institute of Canada (WEICan) at North Cape, PEI and the TechnoCentre Éolien (TCE) at Murdochville, QC.
Accurate wind measurements are a crucial part of any wind energy project. The accurate measurement of wind speed under icy conditions is challenging and demands innovative solutions. Ice accumulation on the cups of an anemometer will change the geometry and since the calibration of this instrument is highly related to its aerodynamic behavior, the accuracy of wind measurements will suffer from icing events. If the ice build-up prevents the instrument from rotating freely, higher loads are seen by the instrument. These high loads can lead to instrument breakdown such as these shown in Fig. 2. Poor wind measurements will affect power production, by delaying the turbine start-up, stopping the wind turbine or not using the right turbine parameters, hence affecting the generated revenues. Poor wind measurements during site assessment will lead to a poor power estimate. Whether measurements in cold climate are needed for turbine operation or site prospecting, there is a need for an instrument designed for such harsh climatic conditions. This research project develops and tests ice-free wind sensors. Up to now, two prototypes were designed and tested. Based on the experience gained and the testing of commercially available heated wind sensors, a third generation was developed and is presented here.
Figure 2: Instruments broken by ice accretions The third generation prototype developed is presented in Fig. 1. The main new feature is the integration of an onboard digital signal processor (DSP). The DSP incorporates a stand-alone heating control and an onboard memory provides sufficient storage capacity for data logging. Any intelligent control algorithm can be implemented whether it is based on meteorological parameters, temperature thresholds, fixed heating, activated from an external source or any other algorithm. Figure 3 presents the power electronics and the DSP printed circuit boards. These components are located inside the anemometer.
Figure 3: Digital signal processor and power electronics printed circuit boards
Figure 4: Heating elements embedded in the cups and tooling used In order to keep the instrument ice-free, heating zones need to be evenly distributed within the instrument. On the third generation prototype, three independent heating zones were targeted. These zones can be independently activated. Obviously, the first heating zone is the rotor (including the cups) where ice build-up can change the aerodynamic behavior of the instrument and hence its calibration. The second heating zone is the shaft of the instrument. Ice build-up in that zone, particularly near the rotor, can affect the rotation of the instrument sometimes leading to complete stop. In that case the wind load on the cups can lead to mechanical failure of the sensor. Infrared thermography imaging of these two zones, independently activated and combined, is shown in Fig. 5. The uniformity of the heating distribution within the cups can be appreciated from Fig. 5, where the heating is applied only to the shaft (left picture), only to the rotor (middle picture) and to both shaft and rotor (right picture). The last heating zone consists of independent heating of the bearings. Preliminary tests showed that these zones were heating as expected.
Figure 5: Thermal imaging of the third generation ice-free prototype Figure 6 presents the surface temperature distribution and the respective power consumption of four ice-free anemometers under a 10 m/s wind flow at -10°C. These instruments are used as reference instruments during anti-icing and deicing testing.
Figure 6: Thermal imaging of several ice-free wind sensors under a 10 m/s wind speed at -10°C Field testing of the third generation ice-free anemometer are taking place this winter (2010-2011) in two different challenging wind test site that are shown on Fig. 7 : - Wind Energy Institute of Canada (WEICan) - TechnoCentre Éolien (TCE)
Figure 7: Map of Canada showing where the field tests are taking place The Wind Energy Institue of Canada (WEICan) located at North Cape, PEI, offers very challenging conditions with high winds and frequent icing events. It is the ideal site for ice-free anemometer field testing. WEICan has strong experience in the wind industry and can provide all the support needed for such experimentation. The device was installed on a boom approximately 10 meters above the ground on WEICan’s main 60 meter meteorological mast as shown in Figure 8. The data gathered from the ice-free anemometer is compared to a non-heated NRG #40C cup anemometer. The instrument behavior is monitored daily and the output of the instrument is compared to the output of several instruments located on the tower. Tests are performed with fixed heating of approximately 75 W. Read about the WEICan field test experience here:
Figure 8: WEICan field test setup The second wind test site is at TechnoCente Éolien located at Murdochville, Québec. The instrument was installed in a 15 m tower and its output is be recorded and compared to other instruments installed at that location (see Fig. 9). These field tests are performed with fixed heating of approximately 75 W.
Figure 9: TCE field test setup In addition, another third generation ice-free anemometer will be used for extensive in-house testing at Université Laval’s test facilities. Research will be oriented on the integration of an intelligent heating control system. Acknowledgement This work would not have been possible without financial support from the Wind Energy Strategic Network (WESNet) and the active participation of the Wind Energy Institute of Canada (http://www.weican.ca/) and the TechnoCentre Éolien (http://www.weican.ca/).
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