Abstract: The minimum pressure head along the upper flat pipe section is recognized as a critical control parameter for ensuring hydraulic safety and operational stability in pumped-storage power stations. A mathematical model for transient flow analysis in the water conveyance system is developed, and a Sobol-based global sensitivity analysis method is incorporated. The influences of upstream surge chamber installation, along with three key design parameters—the inflow-outflow coefficient, throttled orifice diameter, and surge chamber diameter—on the minimum pressure at two selected control cross sections are systematically investigated. The minimum internal pressure at these sections is found to be effectively improved by the provision of an upstream surge chamber, by the optimization of the inflow-outflow coefficient, and by the increase of both the throttled orifice diameter and the surge chamber diameter. Among all influencing factors, the flow variation rate is identified as the dominant variable affecting the minimum pressure at the two sections. By means of the Sobol method, not only the individual effects of each parameter but also their pairwise interaction effects on the minimum pressure are quantitatively evaluated. The sensitivity indices are calculated, and the throttled orifice diameter is shown to exert the most significant influence, followed by the surge chamber diameter and the inflow-outflow coefficient, in descending order. Technical support for the evaluation and optimization of pipeline layout parameters in similar hydraulic systems is provided by the obtained results.

Key words: pumped-storage power station, hydraulic transition, minimum pressure at the upper flat pipe segment, upstream surge chamber