The interaction effect of hydraulic transient conditions of two parallel pump-turbine units in a pumped-storage power plant with considering “S-shaped” instability region: Numerical simulation

In this paper the interaction effect of hydraulic transient flow for two parallel pump-turbine units which are installed on the same penstock, has been numerically investigated. Siah Bishe pumped storage power plant located at the north of Iran, has been considered as the case study. At First, simultaneous emergency shutdown of two units is simulated. Then the state in which the load of unit 1 is rejected while the unit 2 operates normally, has been studied. For this purpose, the governing equations of transient flow in waterways are solved by using the method of characteristics. Since for the same unit speed in “S-shaped” region of pump-turbine characteristic curves, three different values for unit discharge and unit torque are available, the characteristic curves are implemented in the code as the polar form by using modified Suter transformations. Results show that in the case of two units' emergency shutdown, spiral case pressure rise and draft tube pressure reduction, increase by 6.9% and 54.4% in comparison with the one unit emergency shutdown. In the second case, the maximum pressure in the spiral cases and the minimum pressure in the draft tubes decrease by 1.2% and 6.4% respectively. In the recent case, the speed-control governor of unit 2 improves the transient state of the whole system by the wicket gates adjusting.