Continuous Measurements for Detection of Cavitation Caused by Transients in Hydropower Plants and Fluid Transport Systems
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- Institutt for elkraftteknikk 
Surveillance of operating power plants is a progressing science in the hydropower sector. The efficiency improvements are closing in on the limits and reducing the costs by improvement of turbine life time seems to be a profitable approach. Continuously updated knowledge of the state of the mechanical parts of the turbine, will improve the ability to plan and execute maintenance work in a more efficient manner and in more suitable periods. It is therefore an important task to address the challenges connected to determination and quantification of relevant parameters, as well as development of reliable and applicable surveillance systems.This study does an experimental investigation of the coherence between hydraulic transients induced by governing and the relevant parameters used to describe the tendency of cavitation in Francis turbines. Theory relevant to these subjects is inquired to describe the problem sufficiently. An embedded application is built in LabVIEW to acquire and process data during experiments. The application is constructed using the Real-Time module of LabVIEW to investigate how this type of acquisition and data processing can be done in stand-alone surveillance systems. Sub-VIs for Real-Time analysis of acquired data are implemented and tested. Amongst other, a modified Gibsons Pressure-Time method is implemented to do transient flow rate measurements in Real-Time. The ability of the system to control external systems are proved by controlling the speed of an electric motor upon user interaction. The experiment results confirm that hydraulic transient from governing in turbines influence the parameters that describe the conditions for inception of cavitation. Real-Time data acquisition and processing prove its applicability to surveillance of these phenomena in operating turbines. No deduction can be made with regard to detection of cavitation with this experimental set up. The experimental set up may further be used to investigate the frequency response of governing in model turbines. The application built in this study may be developed further and more Real-Time processing methods may be implemented to yield more advanced surveillance systems.