Study On Dynamic Characteristics For Runaway And Load Rejection Process Of Pump Turbine

There is a variety of operating conditions such as power generation,pumping,frequency modulation,and equalization in pump storage power station.Due to frequent conversion between operating conditions,turbine is often in a violent transition process,resulting in instability of the pumped storage unit.Therefore,it is very important to study the transition process of the pump turbine.In this paper,RNG turbulence model is used to investigate the runaway process and the load rejection process of pump-turbine.In runaway conditions,the variation of the model parameters and the operating parameters of the pump turbine was analyzed,which shows that under the non-load runaway conditions,these parameters present the periodic phenomenon of constant amplitude oscillation.The time-frequency characteristics of pressure pulsations of various components were analyzed using Fast Fourier Transform(FFT)and Short-Time Fourier Transform(STFT),and the source of special frequency components in the runaway process was analyzed in conjunction with the internal flow field.Three kinds of frequency components was found in this investigation,including high frequency components with low amplitude,low frequency components with high amplitude,and multiplied components of rotation frequency.The low frequency components is derived from the vortex flow in leafless area.The high frequency components is due to the instantaneous impact of maximum reverse flow in the case of water pump.The multiplied components come from the dynamic and static interference between the runner and the stationary part.Evolution of pressure and streamline in the volute,guide vane,and runner area during the whole transition process is also analyzed.In load rejection conditions,Time-frequency character of pressure pulsations at given position in the whole basin were analyzed.Two low frequency components with high amplitude,two high frequency components with high amplitude,and multiplied components of rotation frequency were found.From the perspective of the performance characteristics and internal flow during the load rejection transition,the causes of these special frequency components were analyzed.It was shown that the direct cause of the instability in load rejection transition is the intense pressure pulsation,and the cause of the instability of the pressure pulsation is the complex vortex flow in the vane and the interior of the draft tube.These vortices at the torqueless condition,conversion point of the working condition and momentary impact condition of the maximum reverse flow are the most intense.