Regulation Characteristics and Load Optimization of Pump-Turbine in Variable-Speed Operation

In order to improve the operating and regulation characteristics of the hydropower unit and to stabilize the load fluctuations, variable-speed pumped storage technology based on converters has been proposed and given more attention recently. However, different from the conventional units, due to the variability of operation conditions, variable-speed units need to develop a load optimization strategy in terms of operating parameter identification to ensure state matching for operation. Therefore, this paper proposes an optimization search step based on the model test curve, and the process of parameter optimization search is elaborated and calculated in the turbine operating condition and pump operating condition, respectively. A mathematical model of the turbine regulation system is established to analyze the influence of speed and guide vane related parameters on the regulation characteristics, and the achievable operating range and regulation capacity in the variable-speed condition is pointed out based on pump-turbine model test, as well as the advantages over the fixed-speed operation. The results show that by applying the load optimization method, the variable-speed unit can be significantly improved in terms of operating efficiency, especially at low head and low power conditions. Meanwhile, a certain range of active power regulation can be realized by the decoupling control of the converter and measuring the guide vane opening in both modes. The analysis of the model test verifies the effectiveness of the variable-speed regulation operation of pump-turbine and provides a reference for the design and operation of the variable-speed hydropower units.

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Turbine mode start-up simulation of a variable speed Francis pump-turbine prototype – Part II: 3-D unsteady CFD and FEM

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/774/1/012070 ◽

2021 ◽

Vol 774 (1) ◽

pp. 012070

Author(s):

D. Biner ◽

S. Alligné ◽

V. Hasmatuchi ◽

C. Nicolet ◽

N. Hugo ◽

...

Keyword(s):

Variable Speed ◽

Pump Turbine ◽

Start Up ◽

Turbine Mode

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Simulation and Experimental Investigation of the Stay Vane Channel Flow in a Reversible Pump Turbine at Off-Design Conditions

Periodica Polytechnica Mechanical Engineering ◽

10.3311/ppme.9345 ◽

2017 ◽

Vol 61 (2) ◽

pp. 94 ◽

Cited By ~ 1

Author(s):

Sandro Erne ◽

Gernot Edinger ◽

Anton Maly ◽

Christian Bauer

Keyword(s):

Transient Flow ◽

Guide Vane ◽

Low Frequency ◽

Rotating Stall ◽

Design Flow ◽

Flow State ◽

Mean Flow ◽

Load Range ◽

Pump Turbine ◽

Stall Inception

This work presents the assessment of the mean flow field and low frequency disturbances in the stay vane channel of a model pump turbine using transient numerical simulations and LDV-based measurements. The focus is laid on transient CFD simulations of characteristic flow states in the stay vane channel when operating at off-design conditions in pump mode. Experimental and numerical investigations obtained a shifting velocity distribution between the shroud and hub of the distributor when continuously increasing the discharge in the part-load range. Simulations captured the occurrence of this changing flow state in the stay vane channel reasonably well. A further increase of the discharge showed a uniformly redistributed mean flow of both hub and shroud side. Monitoring points and integral quantities from measurements and transient simulations were used to interpret the development of transient flow patterns in the stay vane channel at the operating point of strongest asymmetrical flow. During simulation and measurement, a dominant rotating stall inception was observed near the design flow of the pump turbine. At this point where the stall becomes severe, a high level of correlation between the signals of the upper and lower stalled flow in the stay vane channel was calculated. Further simulations for different guide vane positions predicted a strong influence of the guide vane position on the structure of rotating stall.

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Hysteresis Characteristic in Hump Region of a Pump-Turbine Model

10.20944/preprints201608.0007.v1 ◽

2016 ◽

Author(s):

Deyou Li ◽

Hongjie Wang ◽

Jinxia Chen ◽

Torbjørn K. Nielsen ◽

Daqing Qin ◽

...

Keyword(s):

Guide Vane ◽

Pressure Sensors ◽

Low Frequency ◽

Rotational Frequency ◽

Hysteresis Phenomenon ◽

Pump Turbine ◽

Hysteresis Characteristic ◽

Hydraulic Losses ◽

Measurement Direction ◽

Turbine Model

The hump characteristic is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations could be observed, which are harmful to the safe and stable operations and even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), the hysteresis characteristic was found during the hump region. The analysis of performance characteristics reveals that the hump instability is resultant of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of fast Fourier transform confirms that the hump characteristic is related to the low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cease of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis characteristic. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

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Evolutions of guide vane moment of a pump-turbine during runaway transient process after pump trip

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/240/7/072033 ◽

2019 ◽

Vol 240 ◽

pp. 072033 ◽

Cited By ~ 1

Author(s):

Z Y Yang ◽

Y G Cheng ◽

L S Xia ◽

W W Meng ◽

L W Gao ◽

...

Keyword(s):

Transient Process ◽

Guide Vane ◽

Pump Turbine

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Technology Summary on the Application of Variable-Speed Pump-Turbine Units for Wind Storage Operation

2019 IEEE 3rd International Electrical and Energy Conference (CIEEC) ◽

10.1109/cieec47146.2019.cieec-2019123 ◽

2019 ◽

Author(s):

Hao Zhang ◽

Man Chen ◽

Yumin Peng ◽

Jianwei Zhou ◽

Rufei He

Keyword(s):

Variable Speed ◽

Pump Turbine

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Pump to turbine transient for a pump-turbine in a model test circuit and a real size power plant

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/240/7/072039 ◽

2019 ◽

Vol 240 ◽

pp. 072039

Author(s):

S Riedelbauch ◽

C Stens

Keyword(s):

Power Plant ◽

Model Test ◽

Pump Turbine ◽

Test Circuit ◽

Real Size

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Experimental Research on the Rotating Stall of a Pump Turbine in Pump Mode

Water ◽

10.3390/w11112426 ◽

2019 ◽

Vol 11 (11) ◽

pp. 2426

Author(s):

Xue ◽

Liu ◽

Lu ◽

Gao ◽

Meng

Keyword(s):

Flow Field ◽

Experimental Research ◽

Flow Rate ◽

Guide Vane ◽

Rotating Stall ◽

Dynamics Simulation ◽

Positive Slope ◽

Pump Mode ◽

Pump Turbine ◽

Pump Performance

The rotating stall is an unstable flow phenomenon of pump turbines in pump mode, which is of increasing concern to scientists and engineers working on pump turbines. However, at present, various studies are carried out based on CFD (computational fluid dynamics) simulation, while directly measured data and experimental research on flow fields are seldom reported. By utilizing PIV (particle image velocimetry) measuring equipment, the flow field within the guide vane zone of a low specific speed pump turbine in pump mode was measured. By measuring and analyzing the transient flow field, the evolutionary process of the rotating stall within the guide vane passages was determined. We found that for all three tested guide vane openings, regardless of whether the positive slope appeared or not, a pre-stall operating point was found for each opening in the process of decreasing the flow rate. The analysis of the loss within the flow field indicated that the dissipation-induced loss increased greatly after the rotating stall appeared. The pump performance curves at the three guide vane openings showed an inflection at the pre-stall point. When the flow rate is larger than that of the pre-stall point, the head of the pump turbine dramatically increases as the flow rate decreases. However, when the flow rate is smaller than the pre-stall point, such increases noticeably slows down.The research results showed that whether the positive slope on the pump performance curve occurred or not, instability caused by the rotating stall should be of great concern.

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