Evolution and influence of pump-turbine cavitation during load rejection transients of a pumped-storage plant

Pumped-storage power stations play a regulatory role in the power grid through frequent transition processes. The pressure pulsation in the draft tube of the pump-turbine under transient processes is important for safe operation, which is more intense than that in the steady-state condition. However, there is no effective method to obtain the exact pressure in the draft tube in the transient flow field. In this paper, the pressure in the draft tube of a pump-turbine under steady-state and transient conditions are studied by means of CFD. The reliability of the simulation method is verified by comparing the real pressure pulsation data with the test results. Due to the distribution of the pressure pulsation in the draft tube being complex and uneven, the location of the pressure monitoring points directly affects the accurate judgement of cavitation. Eight monitoring surfaces were set in the straight cone of the draft tube and nine monitoring points were set on each monitoring surface to analyze the pressure differences on the wall and inside the center of the draft tube. The relationships between the pressure pulsation value inside the center of the draft tube and on the wall are studied. The “critical” wall pressure pulsation value when cavitation occurs is obtained. This study provides references for judging cavitation occurrences by using the wall pressure pulsation value in practical engineering.

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Experiences on Startup and Trial Operation at Yards Creek Pumped Storage Project

Journal of Basic Engineering ◽

10.1115/1.3571131 ◽

1969 ◽

Vol 91 (3) ◽

pp. 387-395 ◽

Cited By ~ 1

Author(s):

R. J. Swed ◽

K. H. Yang

Keyword(s):

Pump Turbine ◽

Exchange Of Information ◽

Pumped Storage

Many problems were encountered during the startup and trial operation at Yards Creek. This paper describes the major problems and how they were resolved. There are many questions about pump-turbine operation that remain unanswered. Exchange of information and experience is needed. The authors hope that this article will help to stimulate this exchange of information.

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No-Load Stability Analysis of Pump Turbine at Startup-Grid Integration Process

Journal of Fluids Engineering ◽

10.1115/1.4043057 ◽

2019 ◽

Vol 141 (8) ◽

Cited By ~ 1

Author(s):

Ziwen Zhao ◽

Hao Zhang ◽

Diyi Chen ◽

Xiang Gao

Keyword(s):

Stability Analysis ◽

Theoretical Basis ◽

Grid Integration ◽

Integration Process ◽

Pump Turbine ◽

Plant Model ◽

Disturbance Intensity ◽

Pumped Storage ◽

Load Stability ◽

Step Disturbance

This paper focuses on no-load stability during startup-grid integration process. First, no-load operating dynamic character under startup-grid integration process is studied by bifurcation diagram, based on a classical pumped storage plant model. Second, the no-load stability of pump turbine was analyzed by introducing step disturbance and slopes. Finally, the results indicate that the no-load operating point is easy to be disturbed and some factors, such as different disturbance intensity and slopes, have different influence on no-load stability. These methods and results will supply theoretical basis for operating the pumped storage plant steadily.

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The interaction effect of hydraulic transient conditions of two parallel pump-turbine units in a pumped-storage power plant with considering “S-shaped” instability region: Numerical simulation

Renewable Energy ◽

10.1016/j.renene.2017.11.067 ◽

2018 ◽

Vol 118 ◽

pp. 896-908 ◽

Cited By ~ 13

Author(s):

Ali Rezghi ◽

Alireza Riasi

Keyword(s):

Numerical Simulation ◽

Power Plant ◽

Interaction Effect ◽

Instability Region ◽

Pump Turbine ◽

Transient Conditions ◽

Hydraulic Transient ◽

Pumped Storage

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Domain Partitioned Transformation of Pump-Turbine Characteristic Curves in 3-D Space

Volume 1B, Symposia: Fluid Machinery; Fluid-Structure Interaction and Flow-Induced Noise in Industrial Applications; Flow Applications in Aerospace; Flow Manipulation and Active Control: Theory, Experiments and Implementation; Multiscale Methods for Multiphase Flow; Noninvasive Measurements in Single and Multiphase Flows ◽

10.1115/fedsm2014-21738 ◽

2014 ◽

Author(s):

Wei Zeng ◽

Jiandong Yang ◽

Yongguang Cheng

Keyword(s):

Guide Vane ◽

Theoretical Method ◽

Transformation Method ◽

Measured Data ◽

Pump Turbine ◽

Characteristic Curves ◽

Hydraulic Transient ◽

Transient Simulations ◽

Pumped Storage ◽

Conventional Representation

Pump-turbine characteristic curves are the most important boundary condition in the hydraulic transient simulation of a pumped-storage hydropower station. Conventional representation of them, however, has serious defects, For instance, the “S” and “hump” shapes, composed of multiple values and steep twists, lead to the difficulty in interpolation between known guide-vane opening curves, which is necessary in hydraulic transient simulations. Here, a new transformation method was figured out to settle this problem thoroughly and to improve the accuracy of interpolation between the constant opening curves. Prior to the transformation, the characteristic curves are partitioned into eight domains. Curves of each domain were transformed through different formulae that fit the curves well. Eight characteristic surfaces in the 3-D space can be obtained by adding the guide vane opening as the coordinate axis. The theoretical method has been validated by the excellent agreements achieved by comparing the curves interpolated on the characteristic surfaces with the measured data.

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Nonlinear Modeling of Dynamic Characteristics of Pump-Turbine

Energies ◽

10.3390/en15010297 ◽

2022 ◽

Vol 15 (1) ◽

pp. 297

Author(s):

Liying Wang ◽

Kaidi Zhang ◽

Weiguo Zhao

Keyword(s):

Linear Model ◽

Nonlinear Model ◽

Dynamic Characteristics ◽

Clean Energy ◽

Energy Development ◽

Stable Operation ◽

Storage Unit ◽

Pump Turbine ◽

Characteristic Model ◽

Pumped Storage

Hydropower is a kind of clean energy, which can effectively reduce the consumption of fossil energy and is one of the main fields of new energy development. Pumped storage power station not only provides a solution for storing electric energy and generating excess, but also is a clean, efficient, economical and safe power system regulation method with high quality. Accurate modeling of a pump-turbine, as the core equipment of a pumped storage unit, is the key to safe and stable operation of the pumped storage unit. At present, a method of simplifying the external characteristics of a pump-turbine into a first-order linear model is widely used, which cannot effectively and accurately reveal the nonlinear dynamic characteristics of the unit in transition process. In order to meet the demand of high-precision simulation of the unit, a new method of identifying Taylor series expansion considering nonlinearity based on the torque characteristic formula and the flow characteristic formula is proposed, which is applied to the pump-turbine external characteristic model, and retains the second derivative term, making the model a second-order nonlinear model, and thus, the pump-turbine model becomes a nonlinear model. The nonlinear model established is used to simulate the load increase and load rejection of the unit, and the results are compared with those for the linear model. The comparison shows that the nonlinear model established for the pump-turbine can reveal the dynamic response of the unit more effectively and accurately than the linear model, and provide a further guarantee for the safe and stable operation of pumped-storage units, which is of great significance to hydropower energy development.

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Three-Dimensional CFD Simulations of Start-Up Processes of a Pump-Turbine Considering Governor Regulation

Energies ◽

10.3390/en14248507 ◽

2021 ◽

Vol 14 (24) ◽

pp. 8507

Author(s):

Zhiyan Yang ◽

Yongguang Cheng ◽

Ke Liu ◽

Xiaoxia Hou ◽

Xiaoxi Zhang ◽

...

Keyword(s):

Rotational Speed ◽

Three Dimensional ◽

Load Condition ◽

Internal Flow ◽

Pump Turbine ◽

Characteristic Region ◽

Start Up ◽

Speed Fluctuation ◽

Pumped Storage ◽

Cfd Method

The pumped-storage power station is an efficient stability regulator of the power grid. However, due to the instability of the pump-turbine in the S-shaped characteristic region, rotational speed fluctuation is easy to occur in the speed no-load condition, making synchronization with and connection to the grid difficult. To investigate the key factors of these difficult grid connections, the start-up processes of a practical pump-turbine under the lowest head condition were simulated by using the three-dimensional CFD method, in which the governor regulating equations with different regulating parameters were integrated successfully. The results show that the working points oscillate with the fluctuations of rotational speed, discharge, and torque, and different regulating parameters have a significant influence on the dynamic histories. In addition, the internal flow patterns, especially the backflows at the runner inlet, keep apparent values at the middle span (0.5 span) but have regular transitions near the shroud side (0.7–0.8 span). The faster the guide vanes adjust, the faster the backflows change, and the larger the macro parameters fluctuate. Overall, the instability of the start-up is the result of the periodical evolutions of backflows at the runner inlet, because the trend and period of the radial velocities at different inlet span locations are consistent with those of the discharge.

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Deriaz Type Reversible Pump-Turbine Installation at Sir Adam Beck-Niagara Forebay Pumped Storage Project

Journal of Basic Engineering ◽

10.1115/1.4008540 ◽

1959 ◽

Vol 81 (4) ◽

pp. 505-515

Author(s):

A. E. Aeberli

Keyword(s):

Mechanical Design ◽

Operating Conditions ◽

Pump Turbine ◽

Niagara River ◽

Performance Requirements ◽

Start Up ◽

Pumped Storage ◽

Tail Water ◽

Power Project ◽

Turbine Installation

This paper describes the new adjustable blade, single-speed, vertical, single-runner reversible pump-turbine units recently developed and placed into service at Ontario Hydro’s forebay storage pumping-generating station at the S.A.B. Power Project on the Niagara River. The units operate under unusual variations in head. In the pumping sequence the limits are 59 and 90 ft and in the turbine cycle from 45 to 85 ft. Tailwater depression is not required on start-up. Change-over from turbine to pumping sequence is accomplished in a matter of minutes and occurs several times each day. Data are given on the performance requirements for capacity and efficiency versus hydraulic operating conditions of head, tail water, and forebay reservoir levels. Information in the paper includes unusual features of mechanical design.

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