Analysis of wind turbine degradation via the nacelle transfer function

A new method of evaluating the degradation of wind turbine power performance was investigated on Jeju Island, South Korea in compliance with IEC international standards. Evaluating wind turbine degradation fairly within a year is difficult because wind speed varies annually. Thus, three wind turbines on the Hankyeong wind farm were tested to obtain the Nacelle power curves (NPCs) for a period of six years (from 2008 to 2013). The terrain of the wind farm was assessed; furthermore, an 80-m met mast was analyzed along with the nacelle wind speed within the measurement sector to determine the Nacelle transfer function (NTF). Six years of NPCs were determined with the NTFs. On the basis of these curves, each Capacity factor (CF) of the turbines was calculated by applying wind and electric power data derived from the SCADA system. These calculations were compared with the conventional normalized CF. The degradation of the normalized CF was approximately 0.26% per year on average based on the NPCs for the three wind turbines; this degradation was roughly 1.1% when the conventional approach was used.