CAM CORRELATION ANALYSIS USING ACOUSTIC DISCHARGE MEASUREMENT
The low head hydro power plant in Wettingen, Switzerland, is in operation since 1933 and no effective cam optimization has been carried out up to now. The goal of the measuring campaign was to provide data enabling an economic study for a retrofit and upgrade project of the plant and the measurement of the efficiency improvement of turbines after refurbishment. The contribution discusses cam tests using the acoustic transit time method in the intake for discharge measurements. A cam correlation analysis and an efficiency test of the installed Kaplan turbines were performed as a first measurement campaign showing the actual status. While one turbine operated at optimum cam, the other two turbines operated off-cam. After rehabilitation works, based on the recommendations of the first measurements, a second measurement campaign was performed. The results showed the expected efficiency increase due to overhaul of the regulating mechanics (connection between the piston stroke in the machine hall and the regulating ring / guide vane stem at the turbine) of the governor. With the set of data from the second measurement campaign an optimization study for the operation of the three Kaplan units were conducted. Especially the transition zone from one to two and from two to three machine operation could be optimized due to the knowledge of the individual efficiency curves.
Discharge Measurement in a Short Intake with a Converging Section — a Case Study
In the context of a planned retrofit and upgrade of the hydropower plant Wettingen, operated by the Elektrizitätswerke Zürich, three intakes were equipped with acoustic transit time flow measuring devices. Since the flow meters are installed in a converging section, downstream of a pier, it became necessary to perform numerical flow simulations in order to weight the acoustic path velocities for a quantitative flow rate evaluation. With the flow rate available and performing additional site measurements, cam test could be performed with the turbines. While one turbine operated at optimum cam, the other two turbines operated off-cam. Accordingly a substantial improvement potential could be identified.
International Conference on Hydraulic Efficiency Measurements Presentation of optimized integration methods and weighting corrections for the acoustic discharge measurement
According to the appendix of the IEC 60041standard the volume flux Q in a conduit can be determined with the acoustic discharge measurement method by integrating averaged individual path velocity readings. This is done by applying a simplified Gauss-Jacobi integration method, where the individual path readings are weighted and added up. This integration method is then summarized for circular and rectangular sections. The IEC 60041 has the following limitations: First, by assuming a uniform velocity profile, the method cannot cope well with truly turbulent velocity profiles, which fall off at the boundary layers near the wall. To overcome this limitation Voser [3] proposed a modified integration method called OWICS (Optimal Weighted Integration for Circular Sections) with slightly modified optimum sensor positions and weighting coefficients, thus reducing the integration error by 0.1 up to 0.2 percent. Second, the method uses fixed weighting of the averaged path velocities and thus the need for very accurate positioning of the acoustic transducers with respect to the prescribed distances di of the acoustic paths to the pipe centre. Voser [3] also suggested to include the actual, measured path positions for determination of the weighting coefficients and hereby reducing the positioning error strongly.