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

Energies ◽  
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.

scholarly journals A Review of Critical Stable Sectional Areas for the Surge Tanks of Hydropower Stations

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6466
Author(s):  
Wencheng Guo ◽  
Yang Liu ◽  
Fangle Qu ◽  
Xinyu Xu
Keyword(s):  
Electrical Coupling ◽  
Stable State ◽  
Future Research ◽  
Regulation System ◽  
Engineering Practice ◽  
Sectional Area ◽  
Surge Tank ◽  
Power Stations ◽  
Pumped Storage ◽  
Hydropower Stations

The critical stable sectional area (CSSA) for surge tanks corresponds to the critical stable state of hydropower stations and is an important index to evaluate the stability of the turbine regulation system. The research on CSSA for surge tanks is always one of the most important topics in the area of transient processes of hydropower stations. The CSSA for surge tanks provides the value basis for the sectional area of surge tanks. In engineering practice, the CSSA for surge tanks is widely used to guide their hydraulic design. This paper provides a systematic literature review about the CSSA for surge tank of hydropower stations. Firstly, the CSSA for surge tanks based on hydraulic transients is discussed. Secondly, the CSSA for surge tanks based on hydraulic-mechanical-electrical coupling transients is presented. Thirdly, the CSSA for air cushion surge tanks is illustrated. Finally, the CSSA for combined surge tanks, i.e., upstream and downstream double surge tanks and upstream series double surge tanks, is presented. In future research, the CSSA for surge tanks of pumped storage power stations should be explored. The CSSA for surge tanks considering multi-energy complement is worth studying.

scholarly journals Dynamic Safety Assessment in Nonlinear Hydropower Generation Systems

Complexity ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Shuang Li ◽  
Yong Yang ◽  
Qing Xia
Keyword(s):  
Transient Process ◽  
Safety Assessment ◽  
Hydropower Station ◽  
Generation System ◽  
Hydropower Generation ◽  
Safety Level ◽  
Fisher Discriminant ◽  
The Stability ◽  
Evolution Behavior ◽  
Hydropower Stations

This paper focuses on the stability problems in a hydropower station. To enable this study, we consider a nonlinear hydropower generation system for the load rejection transient process based on an existing hydropower station. Herein we identify four critical variables of the generation system. Then, we carry out the dynamic safety assessment based on the Fisher discriminant method. The dynamic safety level of the system is determined, and the evolution behavior in the transient process is also performed. The result demonstrates that the hydropower generation system in this study case can operate safely, which is in a good agreement with the corresponding theory and actual engineering. Thus, the framework of dynamic safety assessment aiming at transient processes will not only provide the guidance for safe operation, but also supply the design standard for hydropower stations.

Runaway Instability of Pump-Turbines in S-Shaped Regions Considering Water Compressibility

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Wei Zeng ◽  
Jiandong Yang ◽  
Wencheng Guo
Keyword(s):  
Elastic Wave ◽  
Stability Criterion ◽  
Simulation Software ◽  
Theoretical Research ◽  
Plant Design ◽  
Stability Criteria ◽  
Pump Turbine ◽  
Characteristic Curves ◽  
Pumped Storage ◽  
The Stability

Pump-turbine characteristics greatly affect the operational stability of pumped-storage plants. In particular, the S-shaped region of the characteristic curves leads to severe instability during runaway conditions with servomotor failure. Thus, this paper aims to investigate the runaway stability criterion by considering all of the important effects in the hydromechanical system. The criterion also helps to judge the S-characteristics of pump-turbines and can provide a guide for plant design and turbine optimization. First, the pump-turbine characteristic curves are locally linearized to obtain formulae for the relative changes of discharge and torque, which depend on the relative changes of rotational speed and water head. Control theory is then applied to analyze the high-order system, by importing the transfer function of the conduits in the elastic mode. Two different kinds of oscillation are found, associated with water inertia and elasticity, based on the established theoretical mathematical model. New stability criteria for the inertia wave in both rigid and elastic modes are developed and compared. The comparison reveals the effect of the water elasticity on runaway instability, which has often been neglected in the previous work. Other effects, such as friction loss and the timescales of water flow and machinery, are also discussed. Furthermore, the elastic wave, which often has a higher frequency than the inertia wave, is also studied. The stability criterion is deduced with analyses of its effects. Based on the stability criteria for the inertia wave and elastic wave, the unstable regions for two waves of the S-shaped curves are plotted. The results are applied to explain the development from inertia wave to elastic wave during transient behavior at runaway conditions. Model tests of runaway conditions were conducted on a model pumped storage station and the experimental data show good agreement with the theoretical analyses regarding the instability of the inertia wave. Further analyses and validations are made based on transient simulations. The simulation software topsys, which uses the method of characteristics (MOC) and a unit boundary represented by a spatial pump-turbine characteristic surface, was applied to analyze the elastic wave. This also supports the conclusions of the theoretical research.

scholarly journals Stability Analysis of Jointed Rock Slope by Strength Reduction Technique considering Ubiquitous Joint Model

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Ruili Lu ◽  
Wei Wei ◽  
Kaiwei Shang ◽  
Xiangyang Jing
Keyword(s):  
Rock Slope ◽  
Reduction Method ◽  
Domain Size ◽  
Jointed Rock ◽  
Strength Reduction ◽  
Hydropower Station ◽  
Strength Reduction Method ◽  
Vertical Side ◽  
The Stability ◽  
Jointed Rock Slope

In order to study the failure mechanism and assess the stability of the inlet slope of the outlet structure of Lianghekou Hydropower station, the strength reduction method considering the ubiquitous joint model is proposed. Firstly, two-dimension numerical models are built to investigate the influence of the dilation angle of ubiquitous joints, mesh discretization, and solution domain size on the slope stability. It is found that the factor of safety is insensitive to the dilation angle of ubiquitous joints and the solution domain size but sensitive to the mesh discretization when the number of elements less than a certain threshold. Then, a complex three-dimension numerical model is built to assess the stability of the inlet slope of the outlet structure of Lianghekou Hydropower station. During the strength reduction procedure, the progressive failure process and the final failure surface of the slope are obtained. Furthermore, the comparison of factors of safety obtained from strength reduction method and analytical solutions indicates that the effect of vertical side boundaries plays an important role in the stability of jointed rock slope, and the cohesive force is the main contribution to the resistant force of vertical side boundaries.

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

2017 ◽  
Vol 29 (5) ◽  
pp. 845-853 ◽  
Author(s):  
Fang Cai ◽  
Yong-guang Cheng ◽  
Lin-sheng Xia ◽  
Yong-qi Jiang
Keyword(s):  
Hydropower Station ◽  
Surge Tank

Numerical Simulation on Rupture Behavior and Selection of Safety Membranes

2014 ◽  
Author(s):  
Chen Sheng ◽  
Zhang Jian ◽  
Xiaodong Yu
Keyword(s):  
Present Theory ◽  
Large Fluctuation ◽  
Surge Tank ◽  
Small Hydropower ◽  
Weak Points ◽  
Maximum Water ◽  
Safety Operation ◽  
Hydropower Stations ◽  
Selection Of ◽  
Rupture Behavior

This present study deals with a new mechanical device consisting of a set of safety membranes, which has been successfully applied in several middle and small hydropower stations in China instead of a surge tank. Safety membranes are installed on the penstock near the powerhouse as controlled weak points. When the pressure caused by load rejection rises to the preset explosive value, one or more membranes rupture, protecting the penstock and the unit from damage. The device is simple, reliable and economical. The method of characteristics is employed to establish numerical model of safety membranes to simulate their rupture behavior, which is then introduced to investigate how to determine the number and diameter of membranes from two aspects, large fluctuation and hydraulic disturbance. The results show that the diameter of the membranes depends on the negative pressure along pipeline under hydraulic disturbance while the number of the membrane depends on the maximum water hammer pressure under large fluctuation during load rejection of the unit. The conclusion of membrane selection can perfect the present theory of safety membranes, and provide the theoretical guidance and practical basis for membrane device design and safety operation.

Intrinsic Thermal Stability of Anisotropic Thin-Film Superconductors

1990 ◽  
Vol 112 (1) ◽  
pp. 10-15 ◽  
Author(s):  
M. I. Flik ◽  
C. L. Tien
Keyword(s):  
Thin Film ◽  
Thermal Stability ◽  
Stability Criterion ◽  
High Temperature Superconductors ◽  
Stability Criteria ◽  
Anisotropic Thermal Conductivity ◽  
Operating Current ◽  
Released Energy ◽  
The Stability ◽  
Thermal Stability Of

Intrinsic thermal stability denotes a situation where a superconductor can carry the operating current without resistance at all times after the occurrence of a localized release of thermal energy. This novel stability criterion is different from the cryogenic stability criteria for magnets and has particular relevance to thin-film superconductors. Crystals of ceramic high-temperature superconductors are likely to exhibit anisotropic thermal conductivity. The resultant anisotropy of highly oriented films of superconductors greatly influences their thermal stability. This work presents an analysis for the maximum operating current density that ensures intrinsic stability. The stability criterion depends on the amount of released energy, the Biot number, the aspect ratio, and the ratio of the thermal conductivities in the plane of the film and normal to it.

The flow of a micropolar liquid layer down an inclined plane

1968 ◽  
Vol 64 (2) ◽  
pp. 513-526 ◽  
Author(s):  
A. J. Willson
Keyword(s):  
Thin Films ◽  
Steady State ◽  
Liquid Layer ◽  
Stability Criterion ◽  
Long Waves ◽  
Inclined Plane ◽  
The Stability ◽  
Micropolar Liquid

AbstractConsideration is given to the flow of a micropolar liquid down an inclined plane. The steady state is analysed and Yih's technique is employed in an investigation of the stability of this flow with respect to long waves. Detailed calculations are given for thin films and it is shown that the micropolar properties of the liquid play an important role in the stability criterion.

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