Sammendrag
This report focuses on power quality and voltage dips, and is based on continuous measurements of voltages and currents from three wind farms for a period of one year. In each of the wind farms there is one measurement point at a single wind turbine, and one for the whole wind farm. The three wind farms utilise different technologies; wind farm 1 consists of fixed speed turbines with directly connected induction generators, and wind farms 2 and 3 have variable speed turbines with synchronous generators (permanent magnet generators in wind farm 3) and full power electronics interfaces. Power quality during normal operation is evaluated by plotting curves for active power slow and fast variations, voltage flicker and harmonics. Significant variations in the output power are seen in all wind farms. While significant 3p fluctuations are seen in the frequency spectrum of the directly connected turbines, the spectrums are damped for the converter interfaced turbines. The standard EN 50160 [1] requires long term severity flicker values ≤ 1 for 95 % of the time, which is fulfilled in all locations. However, a considerable amount of flicker values much larger than 1 is seen in wind farm 1. Voltage dips are evaluated according to EN 50160 [1] , by considering the durations and residual voltages of the positive sequence components of voltage dips. Examples of voltage dip events with corresponding responses in active and reactive power are shown. Some observed differences between the responses of directly connected and converter interfaced turbines are discussed.