Pressure fluctuation analysis and extreme pressure prediction in the transient processes of pumped storage power station

Abstract

The analysis of hydraulic transient process is very important for the design and operation of pumped storage power (PSP) station. The one-dimensional mathematical model is often used in the transient process calculation, by which the maximum value at the spiral case inlet and minimum value at the draft tube inlet can be obtained. However, the one-dimensional mathematical model only provides cross section pressure trends at spiral case inlet and draft tube inlet, and the pressure fluctuation in load rejection cannot be revealed. But the pressure fluctuation amplitude of pump turbine in load rejection process is proved to be huge by test on site. In load rejection test, the measured pressure signals obtained from one or two taps, and the measured pressures affected by tap locations, and polluted by noise. So there exists great difference between the measured extreme values and numerical extreme values. To improve the accuracy of theoretical prediction, analysing the measured data and extracting the pressure fluctuation required in computed results are needed. This paper analyses the load rejection test results in generating mode and pumping mode of a PSP plant using empirical mode decomposition (EMD) method. The measured results at spiral case inlet and draft tube inlet are successfully separated to the trend terms and pulsation terms. Comparison between the measured trends and theoretical calculated results are also performed. The pressure fluctuation value superposed in the transition process calculated result of extreme pressure is recommended, which is of great significance for the safe operation of the PSP station.