Study On Dynamic Characteristics Of Transition Process And Internal Flow Mechanism Of Pump Turbine S Characteristic Area

As a very mature and economical energy storage technology,pumped storage mainly plays the role of load regulation,phase modulation and frequency modulation in power system.The increasing proportion of intermittent energy such as wind energy and solar energy in electric power system puts forward higher demand for energy storage technology.The start-up of pump turbine has a great influence on the operation flexibility and safety of pumped storage power station,and its start-up process is closely related to the "S" characteristic zone of pump turbine.Therefore,it is of great significance to study this problem.In this subject for the study of mechanism of the flow of the pump turbine startup process,refer to the pump turbine model test of a certain pumped storage power station,with the pump turbine model as the research object,based on the Realizable k-epsilon turbulence model,the simulation calculation of pump turbine no-load start the activity in the process of guide vane back stage and increase load transient process.During no-load startup,the wheel speed is controlled by user defined function(UDF),and the process of increasing from 95% rated speed to rated speed is simulated.The moving mesh method is used to realize the displacement of rigid body boundary in the moving guide vane region in the transient process to satisfy the continuous migration of the calculated conditions.For the same transient process,different rotational angular velocity of the guide vane is given to study the influence mechanism of the action of the guide vane on the transient process of the pump turbine.By analyzing the hydrodynamic characteristics of the transient calculation results and the structure of the internal flow,it is found that: The transient calculation results of the starting process of the pump turbine show the characteristic of being far away from the "S" characteristic zone on the full characteristic curve,which is significantly different from its static characteristic.During the no-load startup of the pump turbine,the overall parameters such as the force of the runner and the pressure pulsation in the runner change linearly with the guide vane motion.The unit flow rate changes synchronously with the guide blade movement.When the guide blade stops moving,i.e.the unit flow rate is stable,the transient parameter pulsation value reaches the maximum.The reason is that the working point is closer to the S-shaped region at this time,which is strongly influenced by the "S" characteristic.The torque of the runner decreases with the increase of rotating speed;The load increasing process of pump turbine is shown as a vertical upward straight line starting from the no-load operating point on the full characteristic curve.The flow characteristic changes have undergone an obvious process from the "S" characteristic region to the normal operating range.At the beginning of the loading process,the flow in the unit shows obvious flow characteristics in the "S" characteristic zone,that is,there is a strong vortex flow in the impeller passage.In the process of load increasing,the torque and axial force of the runner increase with the movement of the guide vane.When the guide vane stops moving,the force on the runner remains stable.In the process of load increasing,the pressure pulsation in the flow passage decreases with the increase of load,and the pulsation and the guide vane reach stability synchronously;By comparing the transient calculation results under different rotational angular speeds of guide vanes,it can be found that in the falling process of guide vanes with no load,there exists an angular velocity that makes the guide vanes' movement and the change of the runner's speed completely synchronized.It takes the shortest time for the unit's speed to reach the rated value and the flow is stable.It is suggested that applying the falling speed to guide vane during no-load starting can effectively improve the starting process.The main factor restricting the moving velocity of the guide vane in the process of loading increase is the bearing capacity of the pump turbine unit component to the rate of flow parameter change.That is considering the load bearing capacity of components,a higher load increasing speed can be adopted to effectively improve the flexibility of unit operation without affecting the flow stability.