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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.

This study has analysed the ultimate loads acting on a wind turbine which is operating in a high turbulent flow condition because the ultimate loads are critical factors on the safe design of wind turbine. Since wind flow on the most parts of Korean mountainous are strongly influenced by complex configurations of the topography, turbulence intensity on somewhere is so stronger than an international design standard. For this reason, the characteristics of turbulent wind data collected from actual sites were analyzed and used for the ultimate load evaluation of the wind turbine. With the 270 design load cases on the international standards, the differences of ultimate loads on the wind turbine operating in the standard or high turbulent wind condition are calculated and compared for the an enhanced knowledge of the safe design basis. As are result, it is revealed the specific ultimate loads are strongly affected by the high turbulent wind conditions, thus the characteristics of turbulent flow must be considered during the design of wind turbine.

A comparison study between two performance testing results, one is on the site calibration not needed and the other is needed, was proceeded for the understanding on the effect of site calibration on the complex terrain. As a result, it is revealed that all of uncertainty components is effected by the topographical features dramatically. And the maximum difference of uncertainty reached at around 8% of rated capacity of wind turbine. So, the site calibration is an effective method to remove the variable wind effect by the ground complexity and must be proceeded before the power performance testing of a wind turbine.