Effect of impeller reverse rotation on transient characteristics of pumped-storage unit after pump power-trip

The selection of the guide vane (GV) closure scheme after a pump power-trip (PPT) directly affects the stability of a pumped storage unit during transients. The selection of the GV closure scheme also determined whether the impeller would rotate in the reverse direction. However, the industry has disagreed on whether the impeller should rotate in reverse during the guide vane closing (GVC) process after PPT. To explore whether impeller reverse rotation was beneficial to the GVC process after a PPT, this study adopted a one-dimensional calculation method to select the appropriate GV closure schemes and one- and three-dimensional coupled computational methods to obtain the detailed internal flow field of the selected GVC closure processes. The short-time Fourier transform method was adopted for the time-frequency analysis. The results show that during the GVC process after the PPT, the impeller reverse rotation is conducive to the stable operation of the unit. This finding fills a gap in the relevant research. Moreover, a detailed flow analysis revealed that the impeller reverse rotation improved the unit stability by reducing the rotational speed to weaken the intensity of the pressure pulsation component f_B and shorten its duration. This research finding can guide pumped-storage power stations in determining a more secure GV closure scheme.