Abstract：The low-pressure phenomenon of tail water of a pumped and storage power station has a significant influence on the design of pumped storage power station. In order to clarify the mechanism of low-pressure phenomenon of tail water, based on the water transmission and power generation system of pumped storage power station with one hole and two machines, the low-pressure phenomenon of draft tube in unit during load rejection process was studied by using the rigid water hammer theory. To reveal the mechanism of the influence of the water conveyance system layout of tail water low pressure phenomenon mechanism, the suppression coefficient of unsynchronized flow change was defined, and based on the characteristic line method, the system transition process simulation model was established. By moving the upstream and downstream bifurcations pipe position, the results of different kinds of working condition of load shedding pump storage power station were compared, and the influence of the different changing flow suppression coefficient minimum pressure of the draft tube was studied. The results show that the essence of low tail water pressure is that the flow rate of two units in the same hydraulic unit is not synchronized, which further leads to the alternating change of pressure, and then aggravates the flow rate change process of the unit itself. With the decrease of the inhibition coefficient of flow asynchronism, the phenomenon of flow alternating change and the low pressure of draft tube in the process of load rejection are improved.
