If you are considering future power curve testing, the power curve test report can be used to calculate the valid sector and determine whether site calibration is required for a specified turbine and met mast position. This analysis can be called a “Site Assessment” or “Obstacle and Terrain Analysis.”
If you have not yet picked your test turbines, Openwind can help you pre-screen all turbines. In the upper left part of the window, the user must choose which version of the IEC 61400-12-1 standard and the site layer (“According to Standard” and “Turbine Location”). Next, in the upper right part of the window, the user has a few options to choose for creating preliminary met tower locations (“Automatic Prescreening for All Turbines in Selected Site Layer”). Finally, use the Run Obstacle and Terrain Tests button to calculate preliminary obstacle and terrain analysis results for all turbines using the assumed preliminary met tower location that Openwind has created. This report can help you sort, compare, or down select the possible test turbines based on initial pass/fail terrain result, largest measurement sector, or lowest terrain deviation. From here, the user can more carefully chose an appropriate met tower based on their project requirements and complete the more detailed obstacle and terrain results.
To run the site assessment for a specific test turbine, the user must choose:
•IEC 61400-12-1 Edition 1 (2005) or Edition 2 (2017)
•Test turbine
•Met tower
•Remote sensing device (Optional, Edition 2 only)
When the turbine and met mast(s) are chosen on this screen, Openwind will calculate the distance and check if it is between 2-4D as required.
Openwind will automatically include turbines in the same layout and any neighboring turbine layouts in the obstacle analysis. If there are potential obstacles such as buildings, trees, or parked turbines nearby, the user must configure these first as obstacle layers.
Use the Initialise Measurement Sectors from Obstacle Analysis button to calculate the valid sector and generate the obstacle report. If there were potential obstacles, their relevance (Edition 1 or 2) has been checked in the top part of this report. If they were found to be relevant, Openwind automatically brought them into the second part of the report where the valid sectors are calculated. The valid sectors are calculated for each obstacle’s individual influence on the turbine, met mast, and remote sensing device (if used). The combined valid sector is also shown.
Openwind will pre-populate the combined valid sector into the “Measurement Sector” area at the bottom of the window, in preparation for the terrain analysis. The user can edit the measurement sector if needed.
Use the Run Terrain Analysis (61400-12-1) button to generate the terrain report and output rasters. Openwind creates an output raster for best fit plane, deviation from best fit plane, and measurement sectors.
The plane fitting algorithm used for the power curve terrain analysis is like that for terrain complexity as again the planes are constrained to pass through the turbine base.
Figure 176 shows the slope and terrain variation conditions that are checked for an Edition 1 analysis. Edition 1 only requires that these are checked for the turbine location.
For an Edition 2 test, the terrain requirements are similar but slightly different. The maximum allowable limits for terrain variation are updated, the analysis is repeated for both the turbine location and the met mast location, and there is a new check for 8-16L. The results are also checked for the remote sensing device (if used).
If site calibration is required (Edition 1 or 2), it can be helpful to know what terrain areas caused it. This can be checked quickly in the terrain report, where areas that do not meet the allowable limit are highlighted in red.
Figure 178: Example Terrain Report (Edition 1)
The terrain data can also be checked in more detail with the Openwind output rasters. Select the elevation minus fitted plane layer, then edit the color scale. Set the upper/lower limits to match the upper/lower terrain variation limits. In this example, the allowable limit was ±9.2 m for the 0-2L sector. The areas in pink/brown exceed the allowable limit below/above the plane, and the areas in green are
within the limits. Repeat this step with other terrain areas as needed, since the allowable limits change with L distance.
Figure 179: Viewing Failed Terrain Areas in the Output Raster
