Estimation of hydro turbine-governor system's transfer function from PMU measurements

Generation in the Nordic power system is dominated by large number of hydro power plants, especially in Norway and Sweden. There are indications that, during the last decade, the frequency quality in the system has deteriorated; the number of minutes when the frequency stays outside the permissible range has been increasing. There is ongoing work to find the root of the problem and solutions to improve the quality of frequency. Among other measures, it is important to know the actual dynamic characteristics of the turbine-governor response of power plants. Regarding this issue, the paper presents the work on using state-of-the-art system identification methods to estimate the transfer function of the turbine-governor systems with ambient data. With only PMU measurements at the high voltage side of generator transformers, the identification methods work properly and provide satisfactory estimation.