Toshiya Nanahara

Recently there has been a marked increase in wind power generation. From a power system point of view, because a wind turbine is an intermittent generator with large output fluctuation, any increase in the number of wind turbines gives rise to concerns about the adverse effects of wind turbines on power quality. The smoothing effects of wind turbine output fluctuation are of great importance in assessing the impacts of a large number of wind turbines. This article examines smoothing effects at a wind farm. First it presents a summary of wind measurements taken at two locations with six masts over a period of 1 year on both flat and complex terrain. Then the spatial coherence of wind speed is analysed, paying special attention to its dependence on the distance between observation points, wind direction, wind velocity and fluctuation frequency. Approximation equations for coherence of frequency and distance are obtained by applying Davenport's expression to the observed data. Second, coherence between turbine output at a wind farm is investigated; the results indicate that coherence for wind speed and turbine output shows a considerable resemblance. The article also examines smoothing effects at a wind farm using power spectral density through a theoretical approach. The study proves that smoothing effects can be approximated with a lowpass filter and that the effects at a wind farm should not be taken into account for periods of more than 10 min in case of assessing them on the safe side. Copyright © 2004 John Wiley & Sons, Ltd.

Recently there has been a marked increase in wind power generation. From a power system point of view, because a wind turbine is an intermittent generator with large output fluctuation, any increase in the number of wind turbines gives rise to concerns about the adverse effects of wind turbines on power quality. The smoothing effects of wind turbine output fluctuation are of great importance in assessing the impacts of a large number of wind turbines. With regard to impacts on power system frequency (generation–demand balance), smoothing effects on a power system‐wide scale need to be examined in greater detail, because impacts of wind turbines on power system frequency are dominated by the total power output of wind turbines interconnected to the system. This article examines smoothing effects of wind power output on a power system‐wide scale. First a summary of wind measurements, in which observations were made at 16 sites, is presented. Next, correlation coefficients of wind power output of distant wind turbines are analysed; considerable differences are observed in the correlation coefficients from day to day. Then a new indicator for assessing the smoothing effects—average coherence—is introduced to resolve difficulties of conventional indicators such as coherence. Average coherence is evaluated for the measured data; the results show that smoothing effects among wind farms distributed over some hundreds of kilometres may not be so significant for periods of more than about 100 min. Copyright © 2004 John Wiley & Sons, Ltd.