Influence of the initial working condition on the hydraulic performance of the pump-turbine during runaway transient scenario

Runaway is one of the accident transient scenarios in pumped-storage power stations. During this type of scenario, the pump-turbine operating status varies significantly, inducing increases of pressure pulsations and hydraulic loads on the runner easily. The initial working condition is one of the controlling factors of the runaway scenario, however, its influence on the hydraulic performance of the pump-turbine has not been clear. In this study, the influence was analyzed by the coupled numerical simulations between the one-dimensional pipes and the three-dimensional pump-turbine of a model pumped-storage power system. The results show that the runaway scenario starting from the part-load working condition evidences abrupt variations in the operating trajectory, pressure pulsations, and runner blade radial forces of the pump-turbine; these phenomena do not appear during the runaway scenario starting from the rated working condition. The abrupt variations of the hydraulic performance can be attributed to the transition of runner flow patterns from the stable status to the unstable one during the runaway scenario starting from the part-load working condition. The mechanism of this phenomenon can be attributed to the hysteresis effect of the transient flow patterns, i. e., the instantaneous flow patterns during transients can maintain the corresponding initial flow features to some extent. Therefore, the influence of the initial working condition on the pump-turbine runaway performance should also be considered in the pumped-storage power station, especially when broadening the working range of the pump-turbine. © 2020, China Water Power Press. All right reserved.