Study On Water Level Fluctuation Of The Air Hole Of The Gate Shaft In The Pumped Storage Power Station

With the development of renewable energy,a pumped storage power station has been vigorously developed because of its peak shaving,valley filling,frequency regulation,phase regulation,accident reserve and other functions and advantages in the power grid.The pumped storage power station is a multi-purpose power station,which is characterized by frequent start-up,shutdown and multi-condition changes.Therefore,it is necessary to calculate the transient process of different working conditions and analyze the dangerous working conditions that do not meet the power station standards.In the transient process,the water level of the gate shaft plays a vital role in the safe operation of the unit.In some pumped storage power stations,the phenomenon of water spraying from the air hole will occur during the load rejection because the water level of the air hole exceeds the design value.To avoid this phenomenon,it is necessary to study the change of air hole water level in the transient process of power stations.In this thesis,through the establishment of mathematical models of units,pipelines,gate shaft,upstream and downstream reservoirs,a power station simulation calculation system is formed,which can simulate the transient process of power station.Firstly,the simulation calculation of the transient process of the pumped storage power station is carried out,and the feasibility of the simulation calculation is verified by comparing the calculation results with the field test results.Then,the transient processes of the pumped storage power station with and without diversion surge tank are calculated,and the water level changes of gate shaft and air hole with different areas of gate shaft are compared.The influence of the gate shaft position on the water level changes of gate shaft and air hole is analyzed.The results show that,if the power station has diversion surge tank,no matter how the area of the gate shaft changes,the maximum water levels of the gate shaft and the air hole are basically the same,when there is no diversion surge tank in the power station,the maximum water level difference between the gate shaft and the air hole gradually increases with the increase of the area of the gate shaft.When the gate shaft at different locations,it is found that the greater the distance is between the gate shaft and the inlet,the larger the maximum water level difference between the air hole and the gate shaft is.When the maximum water level of the air hole exceeds the design value,it is necessary to take overflow measures for the air hole.In order to further verify the accuracy of the simulation calculation,a calculation model combining the three-dimensional unsteady flow of the gate well and the onedimensional transient flow of the pipeline is established.The pipeline is calculated by the one-dimensional characteristic line method,and the gate shaft is calculated by the FLUENT software.Using this calculation model,the transient process calculation of the gate shaft system with long pipes on both sides is performed,the details of the dynamic flow field of the gate shaft with free surface and the variations of related parameters are obtained.The comparison of the calculated results with the results of the conventional transient process calculation shows that,if the value of the orifice impedance coefficient is appropriate,the results of the two methods are in good agreement.Therefore,it is proved that one-dimensional simulation calculation is accurate,and a more accurate orifice impedance coefficient can be obtained by this model.