Research On Stability Of Pump Turbine Under The Runaway Condition

Pumped storage power stations are widely used in energy system.It not only undertakes to regulate the load of the power network,but also takes into account the phase modulation and frequency modulation of the power network.At the same time,it also activates the storage and regulation of energy in the new energy supporting facilities.Nowadays,China is vigorously promoting the development of low-carbon,clean energy,Pumped storage power station as a supporting facility for new energy has been vigorously developed.Pumped storage station plays an increasingly important role in national energy balances.In this paper,the reversible pump-turbine in a domestic pumped storage power station is studied.The unstable phenomenon,high-speed water ring,channel vortex and vortex core in draft tube,of the pump-turbine under the runaway condition is studied by the combination of numerical calculation and test.By studying the law of pressure fluctuation in the channel,the generation principle of high-speed water ring,the evolution of the leaf channel vortex and the draft tube vortex,and discussing their effects on the unstable operation of the machine.The main contents and results are as follows:1.Based on the Realizable k-? turbulence model,the flow field in the pump-turbine is simulated.Its internal flow field and external characteristic curve are obtained.Relying on the advanced test rig of the Harbin Institute of Large Electric Machinery,some unstable phenomena(vortex of the draft tube)and four-quadrant operating characteristic curves of the pump-turbine condition were measured.Through the experimental study,the operating characteristic curve of the typical working condition of the pump-turbine and the pressure fluctuation of the corresponding position of the unit are obtained.Comparing the results of the simulation with the results of the test,the simulation results are in good agreement with the test results.It indicates that the three-dimensional full-channel simulation method based on Realizable k-? turbulence model can accurately simulate the runaway condition of pump-turbine.2 Effect of high-speed water ring in vaneless area on stable operation(1)Through the combination of simulation and test,the numerical methods are used to obtain the characteristic parameters of the flow field in the calculation domain of the pump-turbine.The "S" shape characteristic curve was obtained by model test.And the effects of high-speed water rings on the flow in the vaneless region are explored.By analyzing the velocity distribution of the high-speed water ring in the vaneless region,result shows that the position of the high-speed water ring moves toward the runner side as the flow rate increases in the position of the vaneless region.With the opening and flow rate increasing,the high-speed water ring is gradually destroyed and weakened.The water ring is the cause of random fluctuations.(2)The influence of hydraulic excitation on unit operation was studied by ANSYS finite element analysis module.The natural frequency of the runner is obtained by fluidsolid coupling.The relationship between the spatial distribution law of the internal pressure pulsation frequency and the natural frequency is discussed.Under the runaway condition of the pump-turbine,the frequency distribution of the vaneless region is complicated due to the influence of rotor-stator interaction.The pulsation signal of blade-passing frequency and harmonics plays a dominant role in the vaneless region.The hydraulic excitation and the runner structure easily induce resonance.The rotorstator interaction between the runner blade and the guide vane is the main cause of fluidsolid resonance.3.Effect of blade channel vortex on stable operationThrough the transient simulation,the transient flow characteristics are obtained and the evolution process of the coherent structure of the runner region are obtained.The influence of the vortex evolution in the runner on the stable operation of the unit is investigated.The flow in the runner channels is complicated with many different scales vortices in low flow rate runaway condition.These vortices structures are mainly distributed in the inlet region of the blade?the area of the blade trailing edge and the middle section of the runner channels.The vortices structure at the inlet of the runner depends on the change of the attack angle.The flow around the leading edge of the runner inlet and the collision of the fluid at the outlet of the runner opposite to the upstream of the drain cone are the main reasons of the vortex formation at this location.The evolution of the vortex in the runner channel affects the distribution of the blade pressure load.The evolution of the vortex causes the emergence of local low pressure zone and local high pressure zone of blade load.4.Effect of draft tube vortex l vortex on stable operationBy setting monitoring points in the draft tube,the shape of the draft tube vortex of different vane opening conditions is captured.And the influence of the shape and variation characteristics of the vortex on the pressure fluctuation of the draft tube is discussed.The draft tube vortex is closely related to the opening of the guide vane.The evolution of the draft tube vortex is a key factor in the large pressure pulsation in the draft tube.