A study of the wake effects on the wind characteristics and fatigue loads for the turbines in a wind farm

• We analyze wind characteristics changes in a wind farm caused by the wake effect.
• Turbulence intensity and wind shear gradient increase significantly due to wake effect.
• Power performance and fatigue load of typical multi-MW class wind turbine analyzed.
• AEP calculation shows that AEP of Period 2 was much lower than that of Period 1.
• High turbulence intensity due to wake effect significantly increases fatigue load.

With 9 multi-megawatt (MW) wind turbines and a total capacity of 22 MW, Yeongheung Wind Farm is one of the major wind farm projects in Korea. Because there are many wind turbines installed in a small area, the wake effects on the wind turbine power and load need to be investigated carefully.This study analyzes the wind data measured before and after the construction of Yeongheung Wind Farm to examine the wake effect from the wind farm on the mean wind speed, wind shear, and turbulence intensity. Although mean wind speeds were similar in both periods, turbulence intensity and wind shear were significantly increased due to the wake effect by nearby turbines. Power performance and fatigue load analyses of the wind models for each time period were performed using the multi-MW wind turbine model. The wake effect caused the wind speed distribution of Period 2 to be lower than that of Period 1 in the wind speed range of 5–15 m/s, resulting in an about 7% reduction in annual energy production (AEP). Because there was only 0.4% difference in AEP loss between the results obtained using steady and dynamic power curve, we found that the mean wind speed had more influence on AEP than did turbulence intensity. From fatigue analysis, it was determined that the high turbulence intensity and the wind shear gradient in Period 2 caused the high fluctuation of loads, increasing the damage equivalent load (DEL) of Period 2 by 30–50% from Period 1. Although the wind speed distribution of Period 2 was certainly lower than IEC class IIIC, the fatigue loads showed up to 20% higher results for almost all load components. Therefore, we were able to confirm that high turbulence intensity significantly increases the fatigue load.