Superposition control of extreme water levels in surge tanks of pumped storage power station with two turbines under combined operating conditions

This paper investigates the superposition control of extreme water levels (EWLs) in surge tanks of pumped storage power station (PSPS) with two turbines under combined operating conditions (COCs). Firstly, for PSPS with upstream and downstream surge tanks (UDST) and two turbines, the model and ten COCs are presented. The superposition control strategy of EWLs in UDST is designed. Secondly, the most favourable superposition time and the most unfavourable superposition time under COCs, i.e. superposition control moments, are determined. The concepts of initial gradient and superposition gradient are proposed to reveal the control mechanisms. Finally, the influences of tunnel parameters on superposition control moments are analyzed. The results show that tangential points for water level -flow velocity curves of initial operating condition and superposition operating condition are not the superposition control moments. For ten COCs, the most favourable superposition time is the moment of minimum superposition gradient, and the most unfavourable superposition time is con-trary. With the increase of sectional area and decrease of length for tunnel, the superposition control moments decrease. Because the initial gradient and superposition gradient are mainly affected by tunnel parameters, the hydraulic coupling oscillations of UDST have no effect on superposition control moments.

Automated summary

This paper investigates the superposition control of extreme water levels in surge tanks of PSPS with two turbines under combined operating conditions. The control moments are determined by identifying the most favorable and unfavorable superposition times and introducing the concepts of initial gradient and superposition gradient. The influences of tunnel parameters on the control moments are analyzed.