The most common mechanical equipment adopted in the new generation of pumped-hydro power plants is represented by reversible pump-turbines (RPT), required to rapidly switch between pumping and generating modes in order to balance the frequent changes in electricity production and consumption caused by unpredictable renewable energy sources. As a consequence, pump-turbines are required to extend their operation under off-design conditions in unstable operating areas. The paper presents a numerical analysis of the unstable behavior of a pump-turbine operating in turbine mode near the no-load condition. To study in depth the unsteady phenomena which lead to the S-shape of the turbine characteristic, a load rejection scenario at constant and large guide vane opening (GVO) was numerically analyzed by running through the flow-speed characteristic up to the turbine brake region. The flow field analysis led to the onset and development of unsteady phenomena progressively evolving in an organized rotating stall (RS) (65.1% of the runner rotation frequency) during the turbine brake operation. These phenomena were characterized by frequency and time–frequency analyses of several numerical signals (static pressure, blade torque, mass flow rate in blade passages). The influence of the development of these unsteady phenomena on the pump-turbine performance in a turbine operation was also analyzed, and the potential causes that generated the S-shaped characteristic curve were also investigated.

References

References
1.
Ardizzon
,
G.
,
Cavazzini
,
G.
, and
Pavesi
,
G.
,
2014
, “
A New Generation of Small Hydro and Pumped-Hydro Power Plants: Advances and Future Challenges
,”
Renewable Sustainable Energy Rev.
,
31
, pp.
746
776
.
2.
Fisher
,
R.
,
Koutnik
,
J.
,
Meier
,
L.
,
Loose
,
V.
,
Engels
,
K.
, and
Beyer
,
T.
,
2012
, “
A Comparison of Advanced Pumped Storage Equipment Drivers in the U.S. and Europe
,” HydroVision 2012, Louisville, KY.
3.
Zhou
,
J. X.
,
Karney
,
B. W.
, and
Xu
,
J. C.
,
2011
, “
Analytical Study on Possible Self-Excited Oscillation in S-Shaped Regions of Pump Turbines
,”
Proc. Inst. Mech. Eng. A
,
225
(
8
), pp.
1132
1142
.
4.
Gentner
,
C.
,
Sallaberger
,
M.
,
Widmer
,
C.
,
Braun
,
O.
, and
Staubli
,
T.
,
2012
, “
Analysis of Unstable Operation of Pump Turbines and How to Avoid It
,”
Hydro 2012 Innovative Approaches to Global Challenges
, Bilbao, Spain, Oct. 29–31, pp.
1
8
.
5.
Pejovic
,
S.
,
Zhang
,
Q. F.
,
Karney
,
B.
, and
Gajic
,
A.
,
2011
, “
Analysis of Pump-Turbine S Instability and Reverse Waterhammer Incidents in Hydropower Systems
,”
4th International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery Systems
, Belgrade, Serbia.
6.
Olimstad
,
G.
,
Nielsen
,
T.
, and
Børresen
,
B.
,
2012
, “
Dependency on Runner Geometry for Reversible Pump Turbine Characteristic in Turbine Mode of Operation
,”
ASME J. Fluids Eng.
,
134
(
12
), p.
121102
.
7.
Olimstad
,
G.
,
Nielsen
,
T.
, and
Børresen
,
B.
,
2012
, “
Stability Limits of Reversible Pump Turbines in Turbine Mode of Operation and Measurements of Unstable Characteristic
,”
ASME J. Fluids Eng.
,
134
(
11
), p.
111202
.
8.
Seidel
,
U.
,
Koutnik
,
J.
, and
Martin
,
G.
,
2012
, “
S-Curve Characteristic of Pump-Turbines
,”
Hydro 2012 Innovative Approaches to Global Challenges
, Bilbao, Spain, Oct. 29–31, pp.
1
9
.
9.
Wang
,
L. Q.
,
Yin
,
J. L.
,
Jiao
,
L.
,
Wu
,
D.
, and
Qin
,
D.
,
2011
, “
Numerical Investigation on the “S” Characteristic of a Reduced Pump Turbine Model
,”
Sci. China Ser. E
,
54
(
5
), pp.
1259
1266
.
10.
Sun
,
H.
,
Xiao
,
R.
,
Liu
,
W.
, and
Wang
,
F.
,
2013
, “
Analysis of the S Characteristic and Pressure Pulsation in a Pump Turbine With Misaligned Guide Vanes
,”
ASME J. Fluids Eng.
,
135
(
5
), p.
051101
.
11.
Brennen
,
C. E.
,
1994
,
Hydrodynamics of Pumps
,
Oxford University Press
,
Oxford, UK
.
12.
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
.
13.
Hasmatuchi
,
V.
,
Farhat
,
M.
,
Roth
,
S.
,
Botero
,
F.
, and
Avellan
,
F.
,
2011
, “
Hydrodynamics of a Pump Turbine at Off Design Conditions in Generating Mode: Experimental Investigation
,”
SHF Conference on Cavitation and Hydraulic Machines
, Lausanne, Switzerland, May 26–27, pp. 1–4.
14.
Widmer
,
C.
,
Staubli
,
T.
, and
Ledergerber
,
N.
, “
Unstable Characteristics and Rotating Stall in Turbine Brake Operation of Pump-Turbines
,”
ASME J. Fluids Eng.
,
133
(
4
), p.
041101
.
15.
Botero
,
F.
,
Hasmatuchi
,
V.
,
Roth
,
S.
, and
Farhat
,
M.
,
2014
, “
Non-Intrusive Detection of Rotating Stall in Pump-Turbines
,”
Mech. Syst. Signal Process.
,
48
(
1–2
), pp.
162
173
.
16.
Houdeline
,
J.-B.
,
Liu
,
J.
,
Lavigne
,
S.
,
Laurant
,
Y.
, and
Balarac
,
L.
,
2011
, “
Start-Up Improvement in Turbine Mode for High Head PSP Machine
,”
IOP
Conf. Ser.: Earth Environ. Sci.,
15
(
4
), pp.
1
10
.
17.
Yin
,
J.
,
Wang
,
D.
,
Wei
,
X.
, and
Wang
,
L.
,
2013
, “
Hydraulic Improvement to Eliminate S-Shaped Curve in Pump Turbine
,”
ASME J. Fluids Eng.
,
135
(
7
), p.
0711105
.
18.
Yang
,
J.
,
Pavesi
,
G.
,
Yuan
,
S.
,
Cavazzini
,
G.
, and
Ardizzon
,
G.
,
2015
, “
Experimental Characterization of a Pump–Turbine in Pump Mode at Hump Instability Region
,”
ASME J. Fluids Eng.
,
137
(
5
), p.
051109
.
19.
Pavesi
,
G.
,
Cavazzini
,
G.
, and
Ardizzon
,
G.
,
2008
, “
Time–Frequency Characterization of the Unsteady Phenomena in a Centrifugal Pump
,”
Int. J. Heat Fluid Flow
,
29
(
5
), pp.
1527
1540
.
20.
Krause
,
N.
,
Zähringer
,
K.
, and
Pap
,
E.
,
2005
, “
Time-Resolved Particle Image Velocimetry for the Investigation of Rotating Stall in a Radial Pump
,”
Exp. Fluids
,
39
(
2
), pp.
192
201
.
21.
Lucius
,
A.
, and
Brennen
,
G.
,
2011
, “
Numerical Simulation and Evaluation of Velocity Fluctuations During Rotating Stall of a Centrifugal Pump
,”
ASME J. Fluids Eng.
,
133
(
8
), p.
081102
.
22.
Farge
,
M.
,
1992
, “
Wavelet Transforms and Their Application to Turbulence
,”
Annu. Rev. Fluid Mech.
,
24
, pp.
395
457
.
23.
Shao
,
W. Y.
,
2009
, “
Improving Stability by Misaligned Guide Vanes in Pumped Storage Plant
,”
Asia-Pacific Power and Energy Engineering Conference
, Wuhan, China, Mar. 28–31, pp.
1
5
.
You do not currently have access to this content.