Study of Hydraulic Disturbances From Single-Unit Load Rejection in a Pumped-Storage Hydropower Station With a Shared Water Delivery System

The transient characteristics of load rejection process in pumped-storage hydropower (PSH) stations have a close relation to the safety of electric power system and hydraulic facilities. A large portion of PSHs consist of multiple units sharing one tunnel (MUSOT). In this paper, a three-dimensional numerical simulation method for hydraulic disturbance caused by single unit load rejection transition process based on the volume of fluid (VOF) two phase flow model was proposed and a filed test was carried out in a PSH station with a two units sharing one tunnel (TUSOT) setting. The power output from the unit that operates in normal condition (UNC), the pressure fluctuations of the spiral casing inlet and tailrace tunnel outlet, the water level variation and flow pattern in surge tank were obtained through the numerical simulation and field test. The results showed that the highest and lowest water level in surge tank from the numerical method agreed well with the measured data obtained in the field test. The guide vanes closing law of the unit that runs in load rejection (ULR) mainly impacts on the variation of the above parameters. To reduce the influence of single-load load-rejection hydraulic disturbance, a more elaborate guide vanes adjustment scheme of the UNC should be proposed in the next step to avoid large short-time fluctuations in the power output and pressure.