Constant-Speed Oscillation of a Pump Turbine Observed on a Pumped-Storage Model System

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Jinhong Hu ◽  
Jiandong Yang ◽  
Wei Zeng ◽  
Jiebin Yang
Keyword(s):  
Mathematical Model ◽  
Characteristic Curve ◽  
Model System ◽  
Constant Speed ◽  
Negative Slope ◽  
Maximum Deviation ◽  
Pump Turbine ◽  
Storage Model ◽  
Oscillation Process ◽  
Pumped Storage

The hydraulic characteristics of pump turbines in off-design conditions, especially the S-shaped characteristics, are crucial for the safety and stability of the unit. To explore the S-characteristics of pump turbines through a transient method, an experimental investigation was conducted based on a pumped-storage model system at Wuhan University. By shutting down the circulating pump, a special transient process was triggered, forcing the pump turbine to operate in turbine mode, turbine brake mode, and reverse rotational pump mode. As the rotational speed of the pump turbine was maintained almost constant in the oscillation process with a maximum deviation of 0.6%, this transient operation was named as constant-speed oscillation (CSO). The parameters for global performance and pressure pulsations in the vaneless gap were measured and analyzed. In addition, the one-dimensional rigid column theory was used to establish a mathematical model for simulation. The results from simulation were quantitatively compared with the experimental results. Finally, the reason for the CSO was theoretically explained based on stability analysis through the established mathematical model. It was observed that the positive slope of ned–Qed characteristic curves at no-flow resulted in this oscillation. In contrast, the simulation was performed under the same conditions with a modified ned–Qed characteristic curve, which had a negative slope at no-flow. However, the results showed that, with the modified characteristic curve, the pump turbine would stabilize at no-flow.

scholarly journals Internal Mechanism and Improvement Criteria for the Runaway Oscillation Stability of a Pump-Turbine

2018 ◽  
Vol 8 (11) ◽  
pp. 2193 ◽  
Author(s):  
Qin Zhou ◽  
Linsheng Xia ◽  
Chunze Zhang
Keyword(s):  
Energy Dissipation ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Energy Dissipation Rate ◽  
Sharp Change ◽  
Pump Turbine ◽  
Oscillation Process ◽  
Internal Mechanism ◽  
Pumped Storage ◽  
Runaway Process

The runaway oscillation process of the pump-turbine in a high head pumped-storage power plant is usually unstable. The root cause of its instability is still unclear. In this paper, its internal mechanism and the improvement method were studied in depth. First, the flow characteristics in a model pump-turbine during the runaway process at four guide-vane openings (GVOs) were investigated by 3D transient numerical simulations. Then, the energy dissipation characteristics of different types of backflow vortex structures (BFVSs) occurring at the runner inlet and their impacts on the runaway stability were investigated by the entropy production theory. The results show that the location change of BFVSs between the hub side and the mid-span of the runner inlet around the no-load point leads to the sharp change in the energy dissipation rate, which makes the slope of dynamic trajectory positive and the runaway oscillation self-excited. If the occurrence of BFVSs at the hub side is suspended, the runaway process will be damped. Finally, the pump-turbine runner was improved to obtain a wider stable operating range.

scholarly journals Pressure Analysis in the Draft Tube of a Pump-Turbine under Steady and Transient Conditions

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4732
Author(s):  
Jing Yang ◽  
Yue Lv ◽  
Dianhai Liu ◽  
Zhengwei Wang
Keyword(s):  
Steady State ◽  
Pressure Pulsation ◽  
Transient Flow ◽  
Draft Tube ◽  
Simulation Method ◽  
Wall Pressure ◽  
Pump Turbine ◽  
Steady State Condition ◽  
Transient Conditions ◽  
Pumped Storage

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.

scholarly journals Starting generator driving torque modeling in the studies of synchronous starting of synchronous machines

2002 ◽  
Vol 15 (3) ◽  
pp. 399-408
Author(s):  
Zoran Stajic ◽  
Dragan Petrovic ◽  
Dusan Arnautovic
Keyword(s):  
Mathematical Model ◽  
Linear Function ◽  
Polynomial Approximation ◽  
System Model ◽  
Synchronous Machines ◽  
Model Function ◽  
Detailed Model ◽  
Pumped Storage ◽  
Driving Torque ◽  
Time Linear

The paper deals with significance of the starting generator (SG) driving torque modeling in the studies of synchronous starting of synchronous machines (SSSM). The detailed mathematical model of SSSM in reversible pumped storage plant (RPSP) "Bajina Basta" is derived. Because it is very difficult to include the detailed model of the SG turbine in the system model, function of SG driving torque is modeled approximately. The most frequent case in SSSM studies is its approximation with a time linear function, until it reaches the value that should provide rotating of both machine rotors with synchronous velocities, which is also used in the paper Afterwards, three different cases are considered: constant, linear and polynomial approximation in terms of SG rotor velocity. Numerical results obtained by applying developed models to a particular case of synchronous starting are compared with the corresponding experimental results. In this way, it is shown that the application of the most frequently used SG driving torque modeling leads to the erroneous results. The advantages of the polynomial approximation suggested in the paper and its validity is demonstrated.

Constant Speed Motion Simulation and Error Analysis of Planar Non-Circular Curve Parts

2012 ◽  
Vol 220-223 ◽  
pp. 1559-1563
Author(s):  
Rui Wu ◽  
Li Bao ◽  
Yuan Kui Xu
Keyword(s):  
Mathematical Model ◽  
Error Analysis ◽  
Relative Error ◽  
Plane Curve ◽  
Simulation System ◽  
Constant Speed ◽  
Motion Simulation ◽  
Production Practice ◽  
The Mathematical Model ◽  
Circular Curve

The relative direction for a constant speed can be determined according to the planar non-circular curve parts. To establish the mathematical model, a constant speed motion simulation system is designed. The parameters of (vH=5mm/s, δ<3") is commonly used for the simulation system to simulate the movement of drawing the error curve. The results show that by controlling the movement of the plane curve parts in mathematical model can derive the basic constant speed, the relative error of constant speed is less than 3%, it provides a reliable bias when apply to production practice.

scholarly journals A MODEL FOR BREACH GROWTH IN A DIKE-BURST

1988 ◽  
Vol 1 (21) ◽  
pp. 140 ◽  
Author(s):  
Paul J. Visser
Keyword(s):  
Mathematical Model ◽  
The Netherlands ◽  
Laboratory Experiments ◽  
Suspended Load ◽  
Experimental Results ◽  
Sand Transport ◽  
Model Predictions ◽  
Pumped Storage

A mathematical model for sand-dike breach erosion is presented. The heart of the model is a modified Bagnold (1963) energetics—based sand transport conception combined with a simplified Galappatti and Vreugdenhil (1985) pick up mechanism for the suspended load. The model has been tested to three laboratory experiments. The agreement between model predictions and experimental results is surprisingly good. Prototype calculations are presented for the 73 m high sand—dike of a proposed pumped—storage plant in the Netherlands.

Research on Traction Characteristics Model of High-Powered Tractor

2011 ◽  
Vol 143-144 ◽  
pp. 79-84
Author(s):  
Peng Jun Mao ◽  
Wen Jie Gao ◽  
Shui Liang Li ◽  
Chun Yan Hu ◽  
Fu Zhang
Keyword(s):  
Mathematical Model ◽  
Theoretical Basis ◽  
Characteristic Curve ◽  
Traction Force ◽  
Operating Conditions ◽  
Traction Characteristic

Through an analysis of tractor traction balance, a mathematical model which can easily calculate the traction force and efficiency of tractors under different operating conditions was built up, this model offers a basis for tractor-implement matching. Bases on above analyses, the best efficiency rating value was deduced and the traction characteristic curve was also plotted, this study provides a theoretical basis for tractor traction characteristic research.

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

1969 ◽  
Vol 91 (3) ◽  
pp. 387-395 ◽  
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.

A Model for Stall and Surge in Low-Speed Contra-Rotating Fans

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Mohammad Javad Shahriyari ◽  
Hossein Khaleghi ◽  
Martin Heinrich
Keyword(s):  
Rotational Speed ◽  
Current Model ◽  
Characteristic Curve ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Negative Slope ◽  
Initial Slope ◽  
Speed Ratio ◽  
Low Speed ◽  
Fan Performance

This paper reports on a theory for poststall transients in contra-rotating fans, which is developed from the basic Moore–Greitzer theory. A second-order hysteresis term is assumed for the fan pressure rise, which gives the theory more capabilities in predicting the fan instabilities. The effect of the rotational speed ratio of the two counter rotating rotors on the fan performance during the occurrence of surge and rotating stall are studied (the rotational speed of the front rotor is assumed to be kept constant whereas the speed of the rear rotor is variable). One of the new capabilities of the current model is the possibility of investigating the effect of the initial slope on the fan characteristic. Results reveal that unlike the conventional fans and compressors, in the current contra-rotating fan stall cannot be initiated from the negative slope portion of the fan pressure rise characteristic curve. One of the important advantages of the developed model is that it enables investigation of the effect of the rate of throttling on the instabilities. Results show that more the rotational speed of the rear rotor, the more robust to surge (caused by throttling) the fan is.

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

2019 ◽  
Vol 141 (8) ◽  
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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