Modal characteristics analysis of a variable-speed pump-turbine rotor system: a perspective of resonance

Abstract The safety and stability of the rotor system is crucial to the pump-turbine unit. The present paper analyzed the modal characteristics of a variable-speed pump-turbine rotor system based on the rotor dynamics theory and FEM method. The results show that the bending mode of the rotor system exhibits the forms of forward whirling (FW) and backward whirling (BW). The added mass effect will reduce the natural frequency of the rotor system, and it is more obvious for the torsional mode Torsional 1. In addition, the critical speed analysis shows that both the critical speed of the dry mode and wet mode of the rotor system is greater than 700rpm, which proves the safety of the unit. The results of the analysis can be used as a reference for the optimized design of similar variable-speed pump-turbine rotor system, which is conducive to the improvement of the reliability and life of the rotor system.