Looping Dynamic Characteristics of a Pump Turbine in the S shaped Region During Runaway

Abstract

During transients, hydroturbines may demonstrate some dynamic characteristics that differ from the corresponding static characteristics in steady operating conditions. To study the dynamic characteristics of a pumpturbine, we simulated the runaway transients in a model pumpedstorage plant by coupling onedimensional (1D) water conveyance system and threedimensional (3D) pumpturbine. The results show that the runaway dynamic trajectories form loops in the Sshaped region in the unit discharge and unit torque charts of the pumpturbine, not following the corresponding static characteristics. Theoretical analysis and flow patterns comparisons illustrate that the looping trajectories are mainly caused by the successive features of transient flow patterns, namely, the transient flows in the pumpturbine are influenced by their previous status. These features induce different performances between similar dynamic operating points in different moving directions. Furthermore, through comparing the transient parameters calculated by the dynamic and static characteristics separately, we found that both methods are available to capture the unstable behaviors of the pumpturbine, but the dynamic method displays more accurate results when simulating the critical transient parameters. Therefore, in practical engineering applications, we suggest to use the static characteristics method for stability analysis while dynamic characteristics method for transient parameters, which is important for optimizing the layout of water conveyance systems.