Effect of shafting structural unit selection on modal analysis in pumped storage units

Abstract

[Objective] The safe and stable operation of pumped storage units and the avoidance of shafting resonance are essential for pumped storage power stations to effectively meet the regulation demands of new-type power systems. [Methods] Different structural units were selected to study the modal characteristics of the unit shafting in the pumped storage power stations. Based on the finite element method, six rotational speed conditions of 400.0~3 000.0 r/min were selected to conduct a comparative analysis of the sixth-order excitation frequencies and vibration modes of three structural units: independent turbine runner, turbine runner-shaft, and turbine runner-shaft-generator rotor. [Results] The result showed that for different structural units, the natural frequencies and vibration modes of the components were different, though identical vibration modes could occur under different structures. The independent turbine runner structure had the highest sixth-order natural frequency, with no critical speed observed. The runner-shaft-rotor structure had the lowest sixth-order natural frequency, with critical speeds occurring in the first two modes. In the modal analysis of the rotating components of the pump turbine, critical speeds were observed at the 1st and 2nd modes, with speeds of 1 387.1 r/min and 2 164 r/min, respectively. However, when only the runner and shaft components of the pump turbine were considered, the critical speed was observed only at the 1st mode, with a speed identical to the 2nd mode critical speed of the runner-shaft-generator rotor, which was 2 164.0 r/min. The corresponding vibration mode and natural frequency were identical. No critical speed was observed when considering only the runner components of pump turbine. [Conclusion] Therefore, in the modal analysis of the rotating components of the pump turbine, considering the generator rotor and shaft components can more accurately identify the critical speeds of the rotating components and predict the resonance frequencies and vibration modes, which is beneficial for avoiding resonance in the unit. The research findings provide a theoretical basis and engineering support for the design of shafting structure in pumped storage units.

Keywords

pump turbine / modal analysis / vibration characteristic / hydraulic turbine shafting / pumped storage power station