Investigation of the relationship between water quality variations and cavitation occurence in power plants

Abstract

Lab experiments on clean water samples have revealed that water may withstand large tension; a state which could be explained as negative pressure, without occurrence of cavitation. At the same time, one struggles to design hydro power plants that are less susceptible to cavitation; since it limits the range of operation of the power plant. The author has investigated possible effects of water quality variations on cavitation risk, in order to provide better planning of production limits, as well as documenting cavitation events. Hydro power production planning is aimed at maximizing revenue earned from the available water resources, and utilize e.g. weather and power consumption predictions to estimate the current value of water versus its future value. Furthermore, maintenance divisions aim to minimize unnecessary wear on the turbine units, to minimize risk of both unexpected down time and necessary maintenance time. Increased knowledge of the effect of water quality on the maintenance cost of operating a power plant has been one of several motivations for this project. As well as providing data on the presumed effect of water quality on cavitation characteristics, the project is expected to provide useful monitoring tools that may be applied for a wider scope of measurements. The work presented within the thesis consists of experiments in a closed cycle cavitating flow tunnel, as well as long and short term monitoring studies on the medium head Francis turbine at Svorka Power Plant. Methodology is based on and spins further on work done by colleagues in the research group. Main findings are that dissolved gas content has little effect on cavitation inception, but it alters the characteristics of cavitation when other factors are unchanged. The experiments at Svorka also imply that increased suspended particle content may in fact increase risk of cavitation in the sense that cavitation may occur at higher pressures than in clean water cases. We have classified the work in this thesis within three main themes: -Investigate variations of water quality in hydro power plants; across both seasons and due to weather. - Further development of existing cavitation detection algorithms, with special focus on continuous monitoring. - Development of hardware-software integration for cavitation detection and recording. The main contributions are: - Cavitation monitoring knowledge that is important for further studies, and add provided commercial assets for candidate employer - Publication of work on measuring and assessing cavitation risk and operation limits in working hydro power plants. - Increased focus on power plant monitoring, and new advances in less intrusive experimental methods.