Research Papers: Multiphase Flows

Guide-Vane Closing Schemes for Pump-Turbines Based on Transient Characteristics in S-shaped Region

[+] Author and Article Information
Wei Zeng

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

Jinhong Hu

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

Jiebin Yang

State Key Laboratory of Water Resources and
Hydropower Engineering Science,
Wuhan University,
Wuhan 430072, China
e-mail: jbyang830212@whu.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 11, 2015; final manuscript received October 19, 2015; published online January 8, 2016. Assoc. Editor: Frank C. Visser.

J. Fluids Eng 138(5), 051302 (Jan 08, 2016) (11 pages) Paper No: FE-15-1165; doi: 10.1115/1.4032069 History: Received March 11, 2015; Revised October 19, 2015

During the transitional processes of load rejection in a pumped-storage station, the S-shaped characteristics of the pump-turbines can result in relatively large water-hammer and pulsating pressures. These pressures and the high runaway speed during transient processes may directly damage the penstocks and shorten the life of the turbine. In this study, different guide-vane closing schemes for reducing the maximum transient pressures, including the water-hammer and pulsating pressures, and runaway speed were investigated, and the principles for improving the closing schemes were theoretically analyzed based on the transient characteristics in the S-shaped region. First, an analytical expression for the rate of change of relative water head during the transitional processes was deduced based on a simplified mathematical model. It reveals the relationship between the slopes of the trajectory at the pump-turbine operating points (defined as trajectory slopes) and the rigid water-column pressure, which approximates the water-hammer pressure considering compressibility. Then, based on the characteristics of the rigid water-column pressure during the transient process and the effects of guide-vane closure on the trajectory slopes, the selection method for a two-phase guide-vane closing scheme was proposed. The method included the technique for choosing the coordinates of the turning point and the closing speed of the guide vane. Furthermore, the pulsating pressures of pump-turbines were discussed under different working regions and guide-vane openings (GVOs). Considering the characteristics of the pulsating pressures and the runaway speed during the transient processes, the advantage of three-phase valve-closing schemes in controlling the pulsating pressures and the runaway speed was clarified. Finally, a series of model tests were conducted on a pumped-storage station model and the measured data fully validated the correctness of our analyses in this work.

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Fig. 1

Statistics of the number of pump-turbine transitional processes

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Fig. 2

Comparison of rigid and elastic water-hammer models for transient simulations: (a) load rejection with servomotor failure and (b) load rejection with guide-vane closure

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Fig. 3

Validation of elastic model

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Fig. 4

Denominator in term J

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Fig. 5

Comparison of 1/a and Sc: (a) load rejection with servomotor failure and (b) load rejection with guide-vane closure

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Fig. 6

Segmentation of S characteristic curve

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Fig. 7

Relationship between guide-vane closure and trajectory slopes

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Fig. 8

Ladderlike guide-vane closing scheme: (a) guide-vane closing scheme and transient pressure in spiral case and (b) trajectory curve

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Fig. 9

Comparison of fast closing and slow closing of guide vanes during the second phase

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Fig. 10

Spectrograms of pulsating pressures for spiral case of PSS2: (a) 75% load rejection and (b) full load rejection

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Fig. 11

Contour plot of peak-to-peak values of pulsating pressures in spiral case of PSS3

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Fig. 12

Three-phase guide-vane closing schemes and transient pressures in spiral case

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Fig. 13

Comparison of runaway speeds: two-phase closing schemes versus three-phase closing schemes

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Fig. 14

Pumped-storage station model

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Fig. 15

Test of the pump-turbine characteristic curve by transient method

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Fig. 16

Comparison of simulated parameters by topsys and experimental data: (a) pressure in the spiral case, (b) pressure in the draft tube, and (c) rotating speed

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Fig. 17

Comparison of transient parameters of PSS4: two-phase closing schemes versus continuous linear closing

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Fig. 18

Comparison of transient parameters: three-phase closing schemes versus two-phase closing scheme

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Fig. 19

Comparison of trajectories under different closing schemes: (a) test 2 versus test 3, (b) test 2 versus test 4, and (c) test 2 versus test 5



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