Transient Pressure Analysis of a Prototype Pump Turbine: Field Tests and Simulation

Abstract

The transient behaviors of a prototype pump turbine are very important to the safe operation of a pumped-storage power plant. This is because the water hammer pressure during transient events affects the pressure surges in the spiral case (SC) and the draft tube (DT). In addition, the transient pressure pulsations in the vaneless space (VL) are important in the evaluation of the life of the runner. Although several detailed studies have been conducted on the water hammer pressure of a hydropower plant, very few have considered the transient pressure pulsations that occur in the pump turbine. The objective of the present study was to determine the characteristics of the transient pressure pulsations of a 300-MW prototype Francis pump turbine during load rejection and power failure. For this purpose, the frequency features in the steady-state were first analyzed using fast Fourier transform. A Savitzky–Golay filter was then used to extract the water hammer pressure and pulsating pressure from the acquired raw pressure signals. Further, a one-dimensional (1D) method of characteristics (MOC) mathematical model of the pump-turbine was established and used to simulate the transient variations of the flow discharge during transient events, to enable the division of the transient operation conditions into several domains. Finally, the characteristics of the transient pressure pulsations in the SC, vaneless space, and DT were investigated in the time and frequency domains. This paper also discusses the causes of the pressure pulsations that occur under different modes of operation of a pump turbine.