Page 118 - Fluid Power Engineering

96 Chapter Six

The next data management is a recurring task that is performed
daily or with a frequency that coincides with data transfer from tower
to server. This validation of data is a significant task in data manage-
ment. Typical sources of errors and validation issues with measured
data include:

Wear and tear of sensors, booms and mounting, guy wires,

and met-tower
Icing of sensors

Lightning strike

Loose or faulty wiring

In validation check, three tests are performed on the data: 8

Range test: This test identifies values that are outside the val-

idation criteria. Table 6-4 contains a sample of the validation
criteria. The offset is the lowest value recorded by sensor when
the wind speed is below the sensor’s threshold. A reading of
wind speed above 25 m/s does not necessarily mean that the
data is suspect, but it requires a review.
Relational test. This test compares concurrent measured val-

ues of redundant sensors, and sensors at different heights.
If the differences do not meet the validation criteria, then a
review is required. Sample test criteria are in Table 6-5.
Trend test. This test examines temporal changes in measured

values. Sample test criteria are presented in Table 6-6.
After the data issues have been identified, the next step in Fig. 6-13
titled “Validate Data” is executed.

Data Processing
In order to perform statistical analysis of the measured data and to
visualize the data, a variety of data processing methods are used.
For illustration purposes, publicly available wind speed data from a
National Renewable Energy Laboratory (NREL) project in Valentine,
Nebraska, is used in this section. The data is available at heights of 10,
25, and 40 m above the ground level, and for a period of 4 years.
For statistical analysis, the data is organized into bins. An exam-
ple of two-dimensional binning of data is seen in Table 6-7. The two
dimensions for the bins are wind speed and direction. For wind direc-
tion, it is normal to use 16 bins with bin size of 22.5 ; some programs
◦
◦
use 12 bins with bin size of 30 . The wind direction bins are called sec-
tors. Figure 6-14 shows the frequency plot of the North-North-West