Mechanism of air-trapped vertical vortices in long-corridor-shaped surge tank of hydropower station and their elimination

The transient process in the hydropower station with both surge tank and pressure regulating valve is quite complicated and also critical to operation safety. According to the pressure regulating valve working principle, the influence of the valve diameter on the unit speed and spiral case pressure was analyzed theoretically. Mathematical models of the surge tank and pressure regulating valve in the hydropower station were established based on the characteristic method. In a practical engineering, numerical simulation of large fluctuation and hydraulic disturbance transient process are conducted, verifying the correctness of the theoretical analysis. Based on the calculation results, three principles for selecting the valve diameter are concluded: first, making sure the unit speed meet the regulating guarantee requirements when guide vanes fast close; second, the maximum spiral case pressure of two times should be approximate to each other by controlling the superposition of surge wave and water hammer; third, the maximum flow of the valve should be as close to the rated flow of the turbine as possible. The principles are helpful for selecting the valve diameter in similar hydropower station.

Download Full-text

Hydraulic Transients in the Long Diversion-Type Hydropower Station with a Complex Differential Surge Tank

The Scientific World JOURNAL ◽

10.1155/2014/241868 ◽

2014 ◽

Vol 2014 ◽

pp. 1-11 ◽

Cited By ~ 10

Author(s):

Xiaodong Yu ◽

Jian Zhang ◽

Ling Zhou

Keyword(s):

Pressure Difference ◽

Mathematic Model ◽

Hydropower Station ◽

Maximum Pressure ◽

Surge Tank ◽

Hydraulic Transients ◽

Rotating Speed ◽

Spiral Case ◽

Two Sides ◽

Breast Wall

Based on the theory of hydraulic transients and the method of characteristics (MOC), a mathematic model of the differential surge tank with pressure-reduction orifices (PROs) and overflow weirs for transient calculation is proposed. The numerical model of hydraulic transients is established using the data of a practical hydropower station; and the probable transients are simulated. The results show that successive load rejection is critical for calculating the maximum pressure in spiral case and the maximum rotating speed of runner when the bifurcated pipe is converging under the surge tank in a diversion-type hydropower station; the pressure difference between two sides of breast wall is large during transient conditions, and it would be more serious when simultaneous load rejections happen after load acceptance; the reasonable arrangement of PROs on breast wall can effectively decrease the pressure difference.

Download Full-text

Analytical solutions for determining extreme water levels in surge tank of hydropower station under combined operating conditions

Communications in Nonlinear Science and Numerical Simulation ◽

10.1016/j.cnsns.2016.12.012 ◽

2017 ◽

Vol 47 ◽

pp. 394-406 ◽

Cited By ~ 9

Author(s):

Bingbao Wang ◽

Wencheng Guo ◽

Jiandong Yang

Keyword(s):

Analytical Solutions ◽

Water Levels ◽

Operating Conditions ◽

Hydropower Station ◽

Surge Tank ◽

Extreme Water Levels

Download Full-text

Stability Criterion for Mass Oscillation in the Surge Tank of a Hydropower Station Considering Velocity Head and Throttle Loss

Energies ◽

10.3390/en14175247 ◽

2021 ◽

Vol 14 (17) ◽

pp. 5247

Author(s):

Wei Huang ◽

Jiming Ma ◽

Xinlei Guo ◽

Huokun Li ◽

Jiazhen Li ◽

...

Keyword(s):

Stability Criterion ◽

Influencing Factor ◽

Hydropower Station ◽

Velocity Head ◽

Surge Tank ◽

Critical Stability ◽

Basic Equations ◽

Pumped Storage ◽

The Stability ◽

Hydropower Stations

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.

Download Full-text

Study on Dynamic Stability of Large-Scale Underground Cavern Group during Construction Period of Hydropower Station

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.152-154.820 ◽

2012 ◽

Vol 152-154 ◽

pp. 820-825

Author(s):

Wei Ping Nie ◽

Chong Shi

Keyword(s):

Safety Factor ◽

Large Scale ◽

Surrounding Rock ◽

Hydropower Station ◽

Rock Surface ◽

Surge Tank ◽

Large Area ◽

Standard Requirement ◽

Underground Cavern ◽

Main Stress

Taking excavation and supporting of surge tank large-scale underground cavern group of Nuozhadu hydropower station as example, the stability of surrounding rock is analyzed systematically, and the best lining scheme is obtained. Through primary supporting calculation, the displacement and the small main stress increases continuously with excavation of cavern; the rock-point safety factor of decreases continuously with excavation of cavern; the displacement, the small main stress and the rock-point safety factor soon changed when the surrounding rock unloaded suddenly, therefore, the surrounding rock must be supported timely. After excavation, the maximum total displacement is 10.57mm, the maximum tensile stress is far less than the tensile strength of surrounding rock, and the minimum safety factor of key point does not satisfy the requirement of standard; the surrounding rock surface will be broken but not large-area damage basis of excavation. The key point’s safety factor changes and the safety factor satisfies the standard requirement only when the elevation of the second lining larger than this key point. According to lining scheme comparison, the scheme that concrete of surge tank pouring to elevation 625.5m is the most economic and reasonable lining scheme for this engineering.

Download Full-text