Characteristics of pressure fluctuation in pump turbines with splitter blades during the load rejection transient process
In order to reduce the adverse effects of severe pressure pulsations generated during the transition process of the pump turbine on the safety of pumped storage power stations,it is necessary to fully understand the characteristics of pressure pulsation of pump-turbine.This paper conducts an in-depth study on the measured pres-sure data of the pump-turbine with splitter blades during the load rejection transition process.First,a method for extracting time-average pressure and pulsating pressure based on variational mode decomposition(VMD)is presen-ted based on the frequency domain characteristics of pressure pulsations.Then,Fast Fourier Transform(FFT)and Short Time Fourier Transform(STFT)are used to analyze the pulsating pressure at the spiral casing inlet,vaneless area,top cover,and draft tube cone inlet during the stable operation and load rejection of the pump turbine.The general behaviors of frequency composition and time-frequency variation features are revealed during the transition period of steady operation and load rejection of pump turbines with splitter blades.The research shows that the main frequency of the pressure pulsation in the vaneless area of the pump turbine with splitter blades is dominated by the blade passing frequency(BPF)and its half-order harmonics,and the half-order harmonics of the BPF have the characteristics of upstream and downstream propagation.The draft tube inlet pressure pulastion frequency is mainly composed of the low frequency component and the half-harmonic of the BPF.During the load rejection transition process,the BPF and its harmonic frequency in the vaneless area will increase and decrease with time,and the change rule is consistent with the change trend of the runner speed.The method provided in this research presents a novel approach for analyzing collected pressure pulsations and provides a reference for the study of the pressure pul-sation characteristics of pump turbines with splitter blades.It is of great significance to trace the source of the ab-normal vibration of structure and ensure the safe operation of the units.
pump-turbine with splitter bladestransition processpressure pulsationssignal processing
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