The identification of cavitation in Kaplan turbine runner

The presented paper deals with monitoring of cavitation in a Kaplan turbine. The main goal of the experimental works was to verify the suitability of the chosen method for application in the technical diagnostics of water turbines. The experiment was carried out in three different ways, where a correlation was looked for between the results. The first method was the standard method used in water turbine test workbenches. A decrease in efficacy is a manifestation of cavitation. The efficiency drop is evaluated from the energy parameters and cavitation tests are necessary. Simultaneously with the mentioned standard measurement, the formation and development of cavitation in the turbine impeller was monitored by a visualization method and subsequent video analysis. A pulsed light source (stroboscope) with a parallel digital camera was used for visualization. The devices were synchronized via the Timing Hub. The third method used was based on sensing and analyses the acoustic emission in the ultrasonic band. To sense the signal, an ultrasonic probe was used. The probe was tuned in a way that it was not sensitive to vibrations and noise in the audible range. The signal was analysis only in the area of cavitation formation, which was verified by visualizing cavitation areas in the turbine wheel. The results from the experiments showed very good correlation for all three methods. One of the outputs of the experiments is the possibility to use experimental procedures for early diagnosis of cavitation formation. The indisputable advantage of determining the onset of cavitation by sensing acoustic emissions is that it is ab extra disassembly method and at the same time it is not necessary to measure the entire complex of energy parameters.