Analysis of dynamic performance in a pump-turbine during the successive load rejection

Successive load rejection is one of the most crucial transient processes for calculating the maximum pressure in spiral case and maximum rotating speed of runner. One-dimensional mathematical models were established for a pump-storage power station and characteristics method was used to study the successive load rejection. The condition in which the maximum pressure occurs was chosen for three-dimensional unsteady calculation. The boundary conditions at spiral-casing inlet and draft tube outlet were determined by using the one-dimensional result. Based on numerical simulation, the axial hydraulic thrust and transient flow characteristic during the successive load rejection process were analysed. The axial hydraulic thrust during the successive load rejection process was mainly caused by the complex flow in the runner. The complex flow was affected both by hydraulic disturbance and the successive load rejection process.