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Showing content with the highest reputation since 05/21/2015 in all areas

  1. 1 point
    Are there any updated techniques to quantitatively identify periods of dry friction whip in the #40's since the release of the white paper and presentations in May 09?
  2. 1 point
    In light of the findings presented at WindPower 2009, are your recommendations the same or do you have any further suggestions for utilizing data from affected sensors. Since it is apparently so widespread, how do you recommend we treat sensors not part of a pair at the same level but whose serial numbers fall within the affected range?
  3. 1 point
    Q: What is the magnitude of additional uncertainty that a dragging sensor is estimated to cause (%)? A: The magnitude of uncertainty will vary based on the tower configuration and data analysis methodology. We understand that the error can be 1%, but additional data quality checks can reduce this to less than 1%.
  4. 1 point
    Q: Could this problem be found in the non-calibrated #40 anemometers? A: Yes, the same vibratory mode could occur in non-calibrated #40?s manufactured in 2006.
  5. 0 points
    Hello, Thank you for your question. Those sensors were purchased in 2007, and so are currently covered by warranty. When you have cases like this please contact your Sales Account Manager here at NRG, or contact technical support via email (support@nrgsystems.com). All the best, Dave
  6. 0 points
    Great Question! The short answer is that the new 95 inch boom can be used in applications which require lower measurement uncertainty than the 60 inch boom. As for the long answer... I believe you might be looking at Figure G.5 in IEC 61400-12-1 which is based on 2 dimensional Navier-Stokes computations. If so, the figures you indicate are about right (4 tower diameters equates to about a 2.3% centerline disturbance). Another consideration is that the IEC model measures the offset distance as tower centerline to sensor centerline, which really places the 60 inch boom at about 6.5 diameters (for a 10 inch tower) equating to a centerline disturbance of about 1%. However, here is another way to look at it...what level of disturbance is acceptable for your wind resource assessment campaign? Many in the industry would say "let?s make it 0.00%!"... Basically, the further the sensor is away from the tower, the lower the disturbance. In reality, the law of diminishing returns comes into play and no matter how long a boom is (realistically) the disturbance will not (in theory) be 0.00%. At about 10 diameters, the disturbance curve flattens out and approaches horizontal. This is really the sweet spot of boom design as the centerline disturbance is less than 0.5% (some might say it is about 0.3% but I prefer to be a bit conservative). I have also heard that some in the industry believe disturbances are actually greater than what the Navier-Stokes model predicts. If anyone has seen research papers in this area, please add links to this thread! Of course, other design factors are involved such as robustness, cost, ease of installation and transport (the new booms are cost effective, easy to install and are also UPS shippable). In summary, NRG will continue to offer both the 60 inch boom and the 95 inch boom. The new 95 inch boom can be used in applications which require lower measurement uncertainty than the 60 inch boom.
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