Abstract
Surge tanks (STs) are important facilities for ensuring the safety of hydropower stations. Reducing the ST size under the premise of ensuring stable mass oscillations within the ST is the main issue. First, according to the basic equations of the mass oscillation for a hydropower station with an ST, a novel expression of the critical stability section of an ST is deduced considering the velocity head and throttle loss. Then, the sensitivity of each influencing factor of the proposed stability criterion is analyzed. Ultimately, through the simulation of small oscillation transients in two case studies, the water level oscillations (WLOs) in an ST based on three stability criteria are compared. The results show that a 20% smaller ST in a hydropower station may result in 10.4% larger oscillations and a 60% smaller ST in a pumped storage power station may result in 14.3% larger oscillations. Compared with the Thoma criterion and the Chinese specification criterion, the stability criterion proposed in this paper can safely reduce the size of the ST since it considers the influence of the velocity head and throttle loss. The proposed stability criterion can provide an important reference for the optimal design of the STs.
Highlights
The local head loss of the water flowing through the bottom of the Surge tank (ST) is reduced when the ST is equipped with a throttled orifice; that is, αk is reduced, which is not conducive to the stability of the water level oscillations (WLOs) in the ST
To investigate the small oscillation stability of the STs, this paper conducts a theoretical derivation to establishthe a new formula for the critical stability of an this
To investigate small oscillation stability ofsection the STs, paper conducts the influences of the throttled orifice and the velocity head at the bottom of the ST
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Combined with the comprehensive characteristic curve of the turbine, Dong [11] proposed a formula for the critical stability section of the ST considering the influence of the speed governing system and pointed out that the cross-sectional size required for ST stability can be smaller than that of the Thoma criterion by reasonably selecting the speed governor parameters. Guo [21] proposed the critical stability section of ST considering power grid, which contains four terms reflecting the effect of headrace tunnel, penstock, governor and power grid, respectively This formula seems to be inconvenient to apply for the preliminary design because it involves more influencing factors and some of their values are difficult to determine in the preliminary design stage. In the Thoma criterion andare other existing to determine at the preliminary design stage and are not suitable for engineering criteria, only the head losses in the penstock and the diversion tunnel are considered, practice.
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