A fatigue investigation in a Kaplan hydropower station operated in frequency regulating mode

Sammanfattning: Due to the increase of intermittent power in the Nordic grid the need for frequency regulation increases. Hydropower has the ability to respond fast to frequency changes in the grid and is the power source mainly used to regulate the frequency in the Nordic grid. There are different types of frequency regulation and this thesis has focused on primary frequency regulation which purpose is to keep the frequency within the range of ±0.1 Hz from the nominal frequency.For a hydropower station operated in frequency regulating mode the amount of movements in the regulating mechanism increases, especially if it is a Kaplan turbine since it can regulate both the guide vanes and the runner blades. When the hydropower station changes the produced power there are large servomotor forces applied to the regulating mechanism to open or close the wicket gate and the runner blade. During frequency regulation these changes occurs frequently and the risk of fatigue failure increases.The resulting servomotor force in the wicket gate and the runner was calculated from measured data of the servomotor pressure and the dimensions of the servomotors. The angles between the components in the regulating mechanism were calculated knowing the angle of the guide vanes and the runner blades, which was used for translating the servomotor force through the regulating mechanism. The stresses in each component were calculated and the stress cycles were counted which was used to estimate the life time of the components.The larges stresses in the regulating mechanism were found in the runner links and the connecting pins in the runner. In the wicket gate the largest stresses were calculated in the connecting pin between the servomotor and the operating ring, however the stress amplitudes were small, thus fatigue calculations were considered unnecessary. Both the link and connecting pin has an estimated life time which is larger than the commonly used turbine life time of 40-50 years. Even though the life time of the components are above the design criteria it could be improved by implementing a two measure filtering system develop by Voith Hydro.