Use case: Nacelle Transfer Function change

Turbine model: Senvion MM82-2.05MW

In wind turbine performance monitoring, accurate wind speed measurements are crucial for assessing efficiency and energy output. The presented case demonstrates how a visible change in the power curve was traced not to an actual change in turbine performance, but to a shift in the OEM nacelle transfer function (NTF).

Fig. 1 - Comparison between power curves: SCADA Power Curve before the change (blue), SCADA Power Curve after the change (red) and ExpertWind’s corrected Power Curve (green).

Fig. 2 - Average wind speed correction time series. A sudden change was detected and identified as an alteration in the turbine’s NTF.

Initially, an unexpected deviation in the power curve was observed, suggesting a potential performance issue, as illustrated in Fig. 1. However, further analysis based on the Wind Speed Correction values (Fig. 2) obtained from our monitoring prediction models revealed a strong underestimation of the wind speed when compared to a reference behaviour.

The rapid change in the wind measurements, associated with the stability of other key parameters, indicated that the turbine’s measured wind speed had changed, rather than its actual performance. The root cause was identified as an alteration in the NTF—the function that converts raw wind measurements into operational data used by the SCADA system.

The stability in performance is confirmed by the wind speed corrected Power curve (Fig. 1): while the SCADA power curve showed a drop in performance of almost 15%, the corrected one remain within a normal range (+/- 1%).

After receiving these results, the OEM confirmed that an incorrect NTF was being applied to this particular turbine. Once the issue was resolved, both the Power Curves and Wind Speed Correction values went back to the normal and reference behaviour.

By continuously monitoring wind speed measurement, subtle NTF changes can be detected early, ensuring reliable performance evaluation, optimal energy production and remove uncertainties associated with the SCADA wind speed measurements.

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