Abstract
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.
Highlights
Pumped-storage hydropower (PSH) stations offer special functions, such as peak shaving, frequency modulation, phase modulation, emergency standby, and black starts
In the presence of hydraulic connections between units, if some of the units are in full load-rejection operation or the load is drastically increased or decreased, the pressure of the water diversion and tailrace water systems or the water level of the surge tank will fluctuate, affecting the head, flow, and load of units that operate in normal condition (UNC), and the hydropower generators and power grids [5]
To reduce the degree of difficulty of the numerical simulations, only a model for the pump-turbine system of the UNC was considered for the simulations, and the unit that ran in load rejection (ULR) was simplified using the expected flow variations at the spiral casing inlet and the draft tube outlet
Summary
Pumped-storage hydropower (PSH) stations offer special functions, such as peak shaving, frequency modulation, phase modulation, emergency standby, and black starts. Their advantages of startup and shutdown flexibility and their rapid response capabilities ensure the flexibility and safety of the hydropower system and play an indispensable role in ultra-high voltage and smart grids [1]. For cost and technical reasons, most PSH stations share a water diversion tunnel and water tailrace tunnel, which is referred to as multiple units sharing one tunnel (MUSOT). It is of great practical significance to study the dynamic quality and stability of UNC
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