## 2 Test Setup
### Test Turbines and Measurement Instruments  
Table 1 presents the specifications of the wind turbines (no. 1 and 15) tested in this work; they are the same 2-MW wind turbines, HJWT 2000. Their hub height and rotor diameter are 80 m and 87 m, respectively. \begin{table}
\begin{tabular}{c c} \hline \hline
**Category** & **Description** \\ \hline Model & HJWT 2000 \\ Rated power & 2000 kW \\ Hub height & 80 m \\ Rotor diameter & 87 m \\ Swept area & 5944.68 m\({}^{2}\) \\ Rated rotor RPM & 17.3 rpm \\ Power control & Pitch control \\ Cut-in/rated/cut-out wind speed & 3.5/12.5/25 m/s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specification of wind turbines no. 1 and 15 under test. Figure 1: Location of Jeju Island including the layout of wind turbines and instruments at Dongbok wind farm. Table 2 presents specifications of nacelle wind sensors and the supervisory control and data acquisition (SCADA) system. The nacelle anemometers and the nacelle wind vanes were installed on the top of the nacelle, and the wind data were collected by the SCADA system, whose model is Gateway, developed by Mita-teknik. Table 3 shows the specifications of electric power measurement instruments. The current transformer and the power transducer of class 0.5 were used in the wind turbine tower bases in compliance with IEC 61400-12-2. The electric power measured by the instruments was used as power output data in this work. To avoid the flow distortions caused by the rotor blades and the nacelle itself, the nacelle wind sensors should be positioned in accordance with the criteria provided in Annex A of IEC 61400-12-2 [8]. Figure 2 shows the criteria of mounting the nacelle wind sensor and the actual image of the nacelle anemometers and the nacelle wind vanes with a nacelle LIDAR on the nacelle of wind turbine no. 1. The nacelle wind sensors should be mounted above the boundary layer, indicated by the 10\({}^{\circ}\) line from the cylindrical blade root to the profiled blade, and at least 1.5 times the blade root diameter behind the blade root centre. Additionally, they should not be situated within 1 m of the downwind end of the nacelle. According to the criteria, the mounting status of the nacelle anemometers and wind vanes of the wind turbines tested was carefully checked, and it was confirmed that those sensors were properly mounted. \begin{table}
\begin{tabular}{c c c} \hline
**Items** & **Nacelle Anemometer** & **Nacelle Wind Vane** \\ \hline Model & Mita-Teknik WS sensor 690360 & Mita-Teknik WD sensor—0–20 mA \\ Measurement range & 0.5 \(\sim\) 50 m/s & 0 \(\sim\) 360 deg \\ Accuracy & 0.2 m/s & \(\pm\)0.5 deg \\ Data acquisition system & Gateway SCADA system \\ \hline \end{tabular}
\end{table} 
Table 2: Specifications of nacelle wind sensors and the SCADA system. \begin{table}
\begin{tabular}{c c c} \hline
**Items** & **Current Transformer** & **Power Transducer** \\ \hline Model & BC 1009 & P 530 \\ Measurement range & 3000 A & 100–690 V /1–6 A \\ Resolution & Ratio = 3000:5 & 4–20 mA output \\ Accuracy & Class 0.5 & Class 0.5 \\ \hline \end{tabular}
\end{table} 
Table 3: Specifications of electric power measurement instruments. Figure 2: Criteria and actual image for mounting wind sensors with a nacelle LIDAR. Table 4 presents the specifications of the nacelle LIDAR, which is the Wind Iris 2 nd edition developed by Avent. It emits four laser beams as a stream of pulses with four lines of sight, separated by a horizontal angle of 30\({}^{\circ}\) and a vertical angle of 10\({}^{\circ}\). It can measure wind conditions at up to 10 points between 80 m and 400 m horizontally from its optical head. The horizontal wind speed is calculated by taking account of wind shear from 4 beams. In this work, the nacelle LIDAR measurements at 2.5 times the rotor diameter from wind turbine no. 1 were analysed for wind turbine power performance testing.