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Research Papers: Flows in Complex Systems

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

[+] Author and Article Information
Jinhong Hu

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: jinhonghu@whu.edu.cn

Jiandong Yang

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: jdyang@whu.edu.cn

Wei Zeng

School of Civil, Environmental and
Mining Engineering,
University of Adelaide,
Adelaide, SA 5005, Australia
e-mail: w.zeng@adelaide.edu.au

Jiebin Yang

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: 294513358@qq.com

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received November 11, 2018; final manuscript received February 5, 2019; published online March 11, 2019. Assoc. Editor: Kwang-Yong Kim.

J. Fluids Eng 141(5), 051109 (Mar 11, 2019) (13 pages) Paper No: FE-18-1760; doi: 10.1115/1.4042763 History: Received November 11, 2018; Revised February 05, 2019

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.

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Figures

Grahic Jump Location
Fig. 2

Location of pressure sensors

Grahic Jump Location
Fig. 3

Hill chart of the pump turbine

Grahic Jump Location
Fig. 4

Process of CSO test: (a) steady-state operation, (b) shut off circulation pump, (c) pressure in the upstream tank of the pump turbine dropped to a certain critical value and then increased, and (d) sustainable oscillation of water column in the upstream pipe

Grahic Jump Location
Fig. 5

Variation of flow parameters during the CSO test (GVO = 23 deg): (a) upstream pressure, (b) downstream pressure, (c) the net head, (d) rotational speed of the pump turbine, (e) flow discharge, and (f) torque

Grahic Jump Location
Fig. 6

Variations of dimensionless turbine parameters (a) and the dynamic trajectories of nedQed (b) and nedTed (c) characteristic curves during the CSO test (GVO = 23 deg)

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Fig. 7

Pressure pulsations in the vaneless space during the CSO test (GVO = 23 deg) (a) time domain (b) frequency domain

Grahic Jump Location
Fig. 8

Variation of flow parameters in the CSO test with circulation pump restart (GVO = 23 deg): (a) upstream pressure, (b) downstream pressure, (c) the net head, (d) rotational speed of the pump turbine, (e) flow discharge, and (f) torque

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Fig. 9

Simulated results of upstream pressure (a) and downstream pressure (b) from the one-dimensional rigid column theory (GVO = 23 deg)

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Fig. 10

Simulated results of flow discharge (a) and net head (b) from 1D rigid column theory (GVO = 23 deg)

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Fig. 11

Characteristic curves obtained through point-by-point measurement with valve and fitted results (GVO = 23 deg)

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Fig. 12

Variation of flow parameters in the CSO test obtained by shutting off the downstream surge tank. (GVO = 23 deg): (a) upstream pressure, (b) downstream pressure, (c) the net head, (d) rotational speed of the pump turbine, (e) flow discharge, and (f) torque.

Grahic Jump Location
Fig. 13

Comparison of characteristic curves obtained through point-by-point measurement with valve versus artificial modification (GVO = 23 deg)

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Fig. 14

Simulated results of flow discharge (a) and net head (b) from the 1D rigid column theory with modified characteristic curves (GVO = 23 deg)

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Fig. 15

nedQed (a) and nedTed (b) characteristic curves obtained using the CSO and runaway tests (GVO = 23 deg)

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Fig. 16

Reproduction of the loop in nedQed characteristic curve from Fig. 6(b) with revised flow discharge signal (GVO = 23 deg)

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