Instability mechanism and vibration performance of a pumped storage power station under runaway conditions

With the large-scale access of renewable energy to the grid, the load rejection of pumped storage power stations (PSPSs) has become increasingly frequent, thus increasing the possibility of runaway accidents. This study aimed to investigate the instability mechanism and vibration performance of a PSPS by considering the coupling effect of the pressurized pipe and pump-turbine under the runaway condition. First, models of the PSPS based on the elastic water-column (elastic model) and rigid water-column (rigid model) were established. Subsequently, the vibration performances of the elastic and rigid models were compared. The comparison revealed that the runaway instability characteristics of the PSPS were mainly manifested as a high-frequency and large-amplitude vibration caused by the elastic water-column, which was not observed in the rigid model. Therefore, the elasticity of the water-column, which has normally been neglected or simplified using a rigid water-column in previous studies, has a significant effect on the runaway stability. Finally, the effects of other factors on the stability and vibration performance were clarified. The runaway stability was mainly determined by the characteristics of the runaway operating point. The discharge-head relationship coefficient (S5) for quantifying the stability performance of the runaway operating point was extracted. Moreover, increasing pipe friction loss could suppress runaway instability. Additionally, the pipe water inertia only affected the runaway vibration performance but not the runaway stability result. Overall, the study findings deepen the understanding of the physical nature of runaway instability and provide guidance for pump-turbine runner design and stable operation of PSPSs.