Characteristics and Optimization of Transient Process of Pump-Turbine Units in Power Generation Mode

Pumped storage power is considered an ideal regulated power source for new energy. However, the traditional one-dimensional characteristic line method cannot predict the pulsating pressure caused by the reverse “S” characteristic of a pump–turbine. In this paper, a variable-step Euler algorithm is presented to calculate the hydraulic transient process of pumped storage units, the interval times of start-up and load regulation between two pump–turbine units are investigated by using the method of peak staggering and valley filling, and the closure law of guide vanes in the transient process of load rejection is optimized. The results show that the presented method is valid, and that pulsating pressure is accurately captured during the transient process of load rejection. The water level fluctuation amplitude in the surge chamber is greatly reduced by the sequential start-up mode. The rotational speed fluctuation amplitude of the sequential load reduction is also reduced. After the load of two pump–turbine units is rejected at the same time, the duration of pulsating pressure in the spiral case is shortened by 45% by using the quick-then-slow closure law compared with the straight-line closure law. Moreover, the pulsating pressure amplitude and the second peak value of rotational speed are also reduced accordingly, and the transient characteristics of the pump–turbine units are greatly improved.