Research On The Vibration Mechanism Of The Prototype Reversible Pump Turbine

Large pumped hydro energy storage power stations rely on the pump turbines for their two-way operation of pumping and power generation,playing a role of peak-shaving and valley-filling as well as large-scale energy storage in the power grid.The operations of the prototype pump turbine are frequently deviated from rated power and rated water head in order to meet the requirements of peak shaving and incorporate renewable energy into the power grid,which make the whole unit more susceptible to abnormal phenomena,such as large vibrations and so on.Therefore,it has very important scientific value to study the internal flow mechanisms of the pump turbines,such as providing scientific bases on reducing the vibration and pressure fluctuation induced by the internal flow as well as optimizing the design of the flow channel structure.In the present paper,the research object is the prototype pump turbine and the vibration mechanisms of the top cover,the upper and lower brackets in generating,pumping and spin no-load mode are investigated,respectively.Among them,the vibration characteristics of the top cover with load and water head variations are mainly discussed in generating mode.And the effects of lift and excitation current on the vibration characteristics of the top cover,the upper and lower brackets in pumping and spin no-load mode are also discussed.The main findings are as follows:Firstly,it is concluded in the present paper that when the prototype pump turbine is in generating mode,the vibration at the top cover is mainly induced by the pressure fluctuation of the flow-passage parts and is significantly affected by load.Specifically,the whole load range is divided into three regions based on the vibration level and the dominant frequency of the top cover at different load conditions.And the vibration characteristics of the three regions are explained in detail.In addition,water head affects the specific load distribution in the above three regions,but it does not affect the vibration characteristics and dominant frequencies in each region.Secondly,when the prototype pump turbine is in pumping mode,the vibration at the top cover is induced not only by the pressure fluctuation of the flow-passage parts but also by the mechanical aspects of the rotor rotation.The effects of lift on the vibration of the top cover are quite limited.Thirdly,when the prototype pump turbine is in spin no-load mode with excitation current variations,the pressure fluctuation originates in the vaneless space between the stationary guide vanes and the rotational runner.The effects of excitation current on the pressure fluctuation are quite limited.At last,the vibrations of the upper and lower brackets of the prototype pump turbine are mainly induced by the mechanical aspects of the rotor rotation.The hydraulic aspects,load,water head,lift and excitation current negligibly contribute to the vibrations of the upper and lower brackets.