Abstract
Hydraulic pumped storage is a special power generation and electricity shortage technology, which is usually operated with thermal power and nuclear power units, and plays a key role in ultra-high voltage and smart grid. Pressure fluctuations are the main reasons for the instability of the S-shaped region of pump–turbines, which seriously affects their lifespan and operation stability. To reveal the mechanism and propagation law of pressure fluctuations in the S-shaped region as well as numerical simulations at the turbine, the braking and the reverse pump operating conditions of a pump–turbine were carried out. Numerical results were validated using the performance experiments, and the generation mechanism and propagation law of pressure fluctuation were analyzed in detail. The analyses show that high-amplitude pressure fluctuations mainly occur in the braking and reverse pump operating conditions. Under the braking condition, a 0.49-fn low-frequency pressure fluctuation was captured, which is caused by the rotation of the backflow in the vanes. Under the reverse pump condition, a 0.19-fn low-frequency pressure fluctuation was confirmed, which is caused by the periodic rotation of the vortex between the vaneless space. This study has important guiding significance for practical engineering application.
Highlights
In the past decade, the demand for renewable energy has been increasing, and solar power plants and river hydropower stations have been constructed on a large scale, contributing to the protection of water resources and ecosystems [1]
As the main part of pumped storage unit, a pump–turbine has two working states in pump and turbine modes, which need to be constantly switched during operation, resulting in more complex operating conditions
To explore the change in energy in different operating conditions, the study analyzed the hydraulic loss of the turbine, the braking, the runaway, and the reverse pump operating conditions, and determined the main flow components that affect the S-shaped region of a pump–turbine
Summary
The demand for renewable energy has been increasing, and solar power plants and river hydropower stations have been constructed on a large scale, contributing to the protection of water resources and ecosystems [1]. Under different guide vane openings, the unit characteristic curve is S-shaped [9], and the same rotational speed corresponds to multiple discharges, which makes the operating point fluctuate between the turbine condition, the braking, and the reverse pump operating condition. This is the main reason why the power fluctuations occurred in the transient process, and why the grids cannot be connected [10]. To explore the change in energy in different operating conditions, the study analyzed the hydraulic loss of the turbine, the braking, the runaway, and the reverse pump operating conditions, and determined the main flow components that affect the S-shaped region of a pump–turbine. Based on the above analysis, the study will focus on the stay/guide vanes, runner, and draft tube of the pump–turbine
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