Growing environmental concerns and the need for better power balancing and frequency control have increased attention in renewable energy sources such as the reversible pump-turbine which can provide both power generation and energy storage. Pump-turbine operation along the S-shaped curve can lead to difficulties in loading the rejection process with unusual increases in water pressure, which lead to machine vibrations. Pressure fluctuations are the primary reason for unstable operation of pump-turbines. Misaligned guide vanes (MGVs) are widely used to control the stability in the S region. There have been experimental investigations and computational fluid dynamics (CFD) simulations of scale models with aligned guide vanes and MGVs with spectral analyses of the S curve characteristics and the pressure pulsations in the frequency and time-frequency domains at runaway conditions. The course of the S characteristic is related to the centrifugal force and the large incident angle at low flow conditions with large vortices forming between the guide vanes and the blade inlets and strong flow recirculation inside the vaneless space as the main factors that lead to the S-shaped characteristics. Preopening some of the guide vanes enables the pump-turbine to avoid the influence of the S characteristic. However, the increase of the flow during runaway destroys the flow symmetry in the runner leading to all asymmetry forces on the runner that leads to hydraulic system oscillations. The MGV technique also increases the pressure fluctuations in the draft tube and has a negative impact on stable operation of the unit.

References

References
1.
Tanaka
,
H.
, and
Tsunoda
,
S.
,
1980
, “
The Development of High Head Single Stage Pump-Turbines
,”
Proc. IAHR Symp.
,
Tokyo
, pp.
429
440
.
2.
Mei
,
Z. Y.
,
1993
,
Pumped Storage Technology
,
Water Power Press
,
Beijing, China
.
3.
Staubli
,
T.
,
Senn
,
F.
, and
Sallaberger
,
M.
,
2008
, “
Instability of Pump-Turbines During Start-Up in Turbine Mode
,”
Hydro2008
,
Ljubljana, Slovenia
, Paper No. 9.6.
4.
Emmons
,
H. W.
,
Kronauer
,
R. E.
, and
Rockett
,
J. A.
,
1959
, “
A Survey of Stall Propagation—Experiment and Theory
,”
ASME J. Basic Eng.
,
81
, pp.
409
416
.
5.
Tusjimoto
,
Y.
,
Yoshida
,
Y.
, and
Mori
,
Y.
,
1996
, “
Study of Vaneless Diffuser Rotating Stall Based on Two-Dimensional Inviscid Flow Analysis
,”
ASME J. Fluids Eng.
,
118
(1)
, pp.
123
127
.10.1115/1.2817489
6.
Daubechies
,
I.
,
1990
, “
The Wavelet Transform, Time-Frequency Location and Signal Analysis
,”
IEEE Trans. Inform. Theory
,
36
(
9
), pp.
961
1005
.10.1109/18.57199
7.
Loughlin
,
P.
,
Pitton
,
J.
, and
Hannaford
,
B.
,
1994
, “
Approximating Time-Frequency Density Functions via Optimal Combinations of Spectrograms
,”
IEEE Signal Process. Lett.
,
1
(
12
), pp.
199
202
.10.1109/97.338752
8.
Martin
,
C. S.
,
1997
, “
Effect of Pump-Turbines Characteristics Near Runaway on Instability
,”
JSME Centennial International Conference on Fluid Engineering
,
Tokyo, Japan
.
9.
Martin
,
C. S.
,
2000
, “
Instability of Pump-Turbines With S-Shaped Characteristics
,”
Proceedings of 20th IAHR Symposium on Hydraulic Machinery and Systems
,
Charlotte, NC
.
10.
Hasmatuchi
,
V.
,
Roth
,
S.
,
Botero
,
F.
,
Avellan
,
F.
, and
Farhat
,
M.
,
2010
, “
High-Speed Flow Visualization in a Pump-Turbine Under Off-Design Operating Conditions
,”
IOP Conf. Ser.: Earth Environ. Sci.
,
12
(
1
), p.
012059
.10.1088/1755-1315/12/1/012059
11.
Hasmatuchi
,
V.
,
Farhat
,
M.
,
Roth
,
S.
,
Botero
,
F.
, and
Avellan
,
F.
,
2011
, “
Experimental Evidence of Rotating Stall in a Pump-Turbine at Off-Design Conditions in Generating Mode
,”
ASME J. Fluids Eng.
,
133
(
5
), p.
051104
.10.1115/1.4004088
12.
Widmer
,
C.
,
Staubli
,
T.
, and
Ledergerber
,
N.
,
2011
, “
Unstable Characteristics and Rotating Stall in Turbine Brake Operation of Pump-Turbines
,”
ASME J. Fluids Eng.
,
133
(
4
), p.
041101
.10.1115/1.4003874
13.
Zhang
,
L. J.
, and
Wang
,
Z. W.
,
2011
, “
Flow of Pump-Turbine on S-Shaped Region of Complete Characteristics
,”
Trans. Chin. Soc. Agr. Mach.
,
42
(
1
), pp.
42
44
(in Chinese).
14.
Zobeiri
,
A.
,
Kueny
,
J. L.
,
Farhat
,
M.
, and
Avellan
,
F.
,
2006
, “
Pump-Turbine Rotor-Stator Interactions in Generating Mode: Pressure Fluctuation in Distributor Channel
,”
23rd IAHR Symp.
,
Yokohama, Japan
.
15.
Billdal
,
J. T.
, and
Wedmark
,
A.
,
2007
, “
Recent Experiences With Single Stage Reversible Pump-Turbines in GE Energy's Hydro Business
,”
Hydro 2007
,
Granada
.
16.
Shao
,
W. Y.
,
2009
, “
Improving Stability by Misaligned Guide Vanes in Pumped Storage Plant
,”
Asia-Pacific Power and Energy Engineering Conference
,
Wuhan, China
,
IEEE
, pp.
1
5
.10.1109/APPEEC.2009.4918426
17.
Qian
,
Z. D.
,
Zheng
,
B.
, and
Yang
,
J. D.
,
2008
, “
Influence of Misaligned Guide Vanes on Pressure Pulsation in Francis Hydraulic Turbines
,”
Eng. J. Wuhan Univ.
,
41
(
6
), pp.
51
54
(in Chinese).
You do not currently have access to this content.