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6/4/2010
Analysis of Pump-Turbine “S” Instability and Reverse Waterhammer Incidents in Hydropower Systems
Stanislav Pejovic [email protected], Website: www.StanPejovic.com
Qin Fen Zhang Oak Ridge National Laboratory, USA
Bryan Karney Civil Eng. Dept, University of Toronto, Canada
Aleksandar Gajic Faculty of Mechanical Engineering, University of Belgrade, Serbia
4-th International Meeting on
Cavitation and Dynamic Problems
in Hydraulic Machinery and Systems,
October, 26-28, 2011, Belgrade, Serbia
S. Pejovic ‹#›
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There are no failure-free constructions
Ironically, since we learn so much from failures, error-free creation is itself
doomed to fail
BUT
We should learn to balance risks and rewards better both in design and everyday life
Design Context - Preliminary
• Design is almost always tough! – Creating/introducing something new into world
– Must balance completing requirements
– Almost always multi-objective and therefore exposes the values and biases of designer
– Very often includes new and untried elements
– At least partly unexpected consequences
– Certain characteristics make these challenges much worse, many of which are present in hydro design projects …
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Issues requiring further action, and investigations
Areas that require further thought, investigation or attention
Often linked to taking this problem seriously
Not with the presumption that it is a well-known technology
Challenges related to knowledge transfer:
both technically and socially
Hydro systems: in some senses, a well-
known technology, yet….
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KEY THEMES:
Reverse Waterhammer often associated with incidents and accidents
Have no doubt: theoretical aspects are still
uncertain! Need a degree of humility.
Pump-Turbine “S” Instability Additionally Intensify challenges
Verify always by Site Tests
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Design intuition essential! • But system response usually “monotonic”: the large the load, the greater the risk.
In these cases, we know where safety lies! If we assume larger external loads in the design than can be realistically expected, we will be safe… But not so in many hydro-turbine applications! Sometimes small variations have big consequences!
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Case 1: Accident at Russia’s Biggest Hydroelectric Associated with water column separation, a phenomena notoriously non-monotonic…
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Accident
75 dead
Draft tube water column separation
2009 S. Pejovic ‹#›
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Accident at Russia’s Biggest Hydroelectric
Sayano-Shushenskaya – 2009 August 17 S. Pejovic ‹#›
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Unit 2
Units 7 and 9
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Generator Upper Bearing
Generator rotor
Destroyed column
Enclosed Bus
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After the Accident
Air-Oil Tanks
Sump Tank
Crosshead – Unit 2
Colector Ring
Unit 1
Unit 2
Floor
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Krivtchenko G. I., Arshenevsky N. N., Kvyatkovskaya E. V., Klabukov V. M. (1975), Hydraulic Transients in Hydroelectric Power Plants, (in Russian), Energia, Moscow.
Yet a Russian (former USSR) book (the only book; none in English!) analyzes reverse waterhammer!
Most severe catastrophe occurred in Russia
The implications are profound: it is too expensive to make our own mistakes; we much learn efficiently from others:
We must read We must learn We must teach
Laboratory tests in Moscow
Flow Diagram
Real problem Physical model
Assumptions
Simplification Assumptions
Simplification
Mathematical model
Assumptions
Simplification
Computer program
Input data
Output (results)
Analysis
Simplifications Verification
Conclusions
Recommendations
Accuracy
Lab model
Assumptions
Simplification
?
?
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Case 2 and 3
Kaplan turbine accident
Water column separation
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Case 2: Design implications are even harder
when system unpredictability is coupled with
complacency or the presumption that the
problem is already solved
Hydroelectric station Zvornik
Former Yugoslavia Pejovic S., Krsmanovic Lj., Gajic A., Obradovic D., Kaplan Turbine Incidents and Reverse Waterhammer, Water Power and Dam Construction, 1980, pp. 36-40.
… Gajic A., Pejovic S., Ivljanin B., Reverse Waterhammer - Case Studies, Proceedings of the International Conference on CSHS03, Belgrade, 2003
18
Kaplan turbine accident
Water column separation
Runner blade broken
Power 22 MW
Head 19 m
Speed 150 rpm
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Case 3: Some design stories are hard to tell! Details not known, but only a year later…
Former Yugoslavia
Unpublished case
Hydroelectric station Ozbalt
Case 4 and 5: Already completed and
successful designs doesn’t mean the
problem is understood going forward!
Kaplan turbine accident again involves
water column separation
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Case in Russia published: 1. Time V.A. (1960). Reverse Water Hammer in the Kaplan Turbine Drat Tube (in Russian). Electricheskie Stancii, No 3, 1960.
2. Zmudj A.E., Litkovskii J.A., Rubek N.N. (1960). Reverse Waterhammer in Hydroelectric Plants (in Russian),
Gidroelectromashinostroenije, No 2, 1960.
Unpublished case in the US: Ice Harbor turbine No. 2
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Russia published accident
Case 4
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US unpublished Kaplan turbine accident:
Ice Harbor turbine No, 2
Case 5
Case 6: Systems with pathological response deserve extra care!
“S” Unstable Zone
Hydraulic resonance
Penstock accident
23 S. Pejovic
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1995
ACCIDENT
Running in
“S” Unstable Zone
Martin C,S., Post Accident Report, Frequency, Resonance, and Hydraulic Transient Analysis, Bhira Pumped Storage Installation, The Tata Power Company Limited, 1996.
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Case 7
“S” Unstable Zone
Runner is jumping up at full load. 2001
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• http://www.chincold.org.cn/dams/rootfiles/2010/07/20/1279253974149477-1279253974151981.pdf
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Turbine unit data Power 300.0 MW GD2 4100 t· m2 Rated speed nr 500.0 r/min Runner diameter D1 4.080 m D2 2.045 m Rated head Hr 526.0 m Rated flow Qr 67.7m 3/s Rated Turbine output Pr 306.0 MW Max. output Pmax 337.0 MW Unit installation EL 225.0 m
S. Pejovic http://www.power-technology.com/projects/tianhuangping/
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Very low specific speed
• Nq 37
• Runner is jumping up at full load.
2001 Why?
℃)
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H
35
• Construction began in 1994 and the plant came online in 2001
• Estimated cost of $1.08 billion.
• The first generator began operation in October 1998,
• The remaining five 306MW units came online in stages during 1999 and 2000.
• Power station produces 316 million MWh of electricity a year
• http://www.power-technology.com/projects/tianhuangping/
US$600 per kW
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L
Case 8
Water column separation
indicated at construction stage. 1997/1998
Catastrophe prevented at trial operation.
2004
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Canadian Internationals Consortium
Many reports indicated water column separation as extremely catastrophic phenomenon.
1997/1998 S. Pejovic ‹#›
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Masjed-e Soleyman Commissioning tests
Main features of load rejection
2002/2003
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Transient problems upon load rejection
Masjed-e Soleyman case study
Air injection mitigates
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Case 9: Complexity doesn’t preclude successful completion and reasonable operation.
“S” Unstable Zone
Water column separation
“S” instability discovered at design stage by designer
Confirmed by manufacturer
Prevented on time!
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Pumped storage Bajina Basta (1982). Turbine:
Head: 497 - 600 m | Rated head: 554 m Output: 243 - 315 MW | Rated output: 249 MW
Speed: 428.6 rpm
Specific speed: 73 m-kW
Pump: Head: 532 - 621 m
Discharge: 37 - 51 m3/s
Speed: 428.6 rpm
Specific speed: 27 m- m3/s
Runaway speed: 659 rpm
Transient speed rise after full load rejection: 45%
Maximal penstock pressure: 900 m
Submergence: 54 m
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Bajina Basta pumped storage plant
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Bajina Basta pumped storage plant Two units runaway One units runaway
6 b
ar
1975
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Bajina Basta pumped storage plant Project design procedure
S Pejovic responsible for hydraulic design
1.Feasibility study,
2.General design,
3.Detailed design (after bidding),
4.Commissioning and running-in process,
5.Analysis after 30 years
Why???
Why?
team designing the pump-turbines
3.Detailed design (after bidding),
4.Commissioning and running-in process
team designing the plant
1. Feasibility study,
2. General design,
3. Detailed design (after bidding),
4. Commissioning and running-in process
S. Pejovic ‹#›
“S” instability and water column separation
S Pejovic responsible for hydraulic design 1.Feasibility study,
2.General design,
3.Detailed design (after bidding),
4.Commissioning and running-in process,
5.Analysis after 30 years
“S “ form characteristics and resonance at runaway
Discovered and
published 1976
Discovered and
published 2010
Turbine “S” Instability Huge Risk for Draft Tube Water Column Separation
Verified, proofed;
published 1984 “S “ form instability
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0.11𝛥ℎ𝑚𝑎𝑥 =g
ue
2
2
max
0.11Δhmax=
g
ue
2
2
max
Masjed-e-Suleyman Hydroelectric Project, Iran
(2000 MW; eight units each 250 MW)
1997 / 1998 • Review previous projects
• Review manufacturers booklets and drawing
Explicitly have indicated troubles in the long tailrace tunnels (480 m)
Why analysis after 30 years? New experience; lessons learned
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Canadian Internationals Consortium
“Water column separation must be prevented …”… reports has begun.
Only team leader has believed me and supported reports. Others involved in the project have not believed that rejoining of separated water columns can be dangerous catastrophic case
Draft tube measured peak pressure jump 41 m = 130 ft = 4.1 bar
Two units operate as turbines, developing 298 MW each
unit 1 load rejection, wicket gates close down
unit 2 continue normal operation
Other dangerous cases of normal operation should have been
analyzed
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Bajina Basta
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Comparison 4
bar
Bajina Basta
Masjed-e Soleyman
Dra
ft t
ub
e P
ress
ure
One unit load rejection
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4 b
ar
Masjed-e-Suleyman Turbines
Tailrace tunnel 480 m
Bajina Basta Pump-turbines
Tailrace tunnel 300 m
Dra
ft t
ub
e P
ress
ure
Draft tube measured peak pressure jump 410 m = 1300 ft
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ASME - American Society of Mechanical Engineering HPTC - Hydro Power Technical Committee
In 2008 this recognized as dangerous rejoinder of separated water columns in the draft tube and runner!!!!!!
This is not most dangerous case
The Guide to Hydropower Mechanical Design HCI Publication, 1996, new edition under review
2011
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Hydraulic transient analyses are always very approximate! Main reasons:
Untrue similarity Mathematical instability
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Mathematical instability
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Transient flow in close conditions is represented by equations of motion and continuity
02
cc
Dt
c
x
cc
x
hg
0
2
x
zc
x
c
g
a
x
hc
t
h
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Pump-turbine dynamic equation of rotation
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“S” instability HDm
dt
dnJ 4'
1
'
1
30
HDmdt
dnJ 4'
1
'
1
30
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• Machine enters dangerous reverse pump operation characterized with strong vibrations, hydraulic unstable vortices, multiphase cavitation.
• Unit-1 follows the “S” shaped curve far in fourth quadrant, goes back under curve of zero efficiency, etc.
• Unit-2 remains in narrow range around initial point 300 MW
Reverse pump
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Technologies are interlinked and must be continually transferred and elaborated in order to work innovations are disparate if they are blocked by continuous gaps in our mutual conveyance of knowledge.
Reminders: what models are and are not •Physical models approximate •Mathematical models approximate •Computer iteration - solutions not always accurate Input data There are no similarity for transient and multi phase flows •Measured machine characteristics approximate •Valve and gate measured data approximate •Wave speeds inaccurate In draft tubes: air content, velocity and pressure distribution, oscillating unstable vortex core and measurement difficulties further reduce accuracy
“S” instability, more troubles
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Description of Reality Modeling life in mars
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Conclusion • As design is problematic and consequences can be dramatic • At least two independent experienced teams should design electric plants • All projects should be reviewed by experienced experts
Design procedure 1.Feasibility study – balancing overall tensions
2.General design – converging the feasible
3.Detailed design (after bidding) – the devil in the details
4.Commissioning and running-in process – still being alert and never complacent – expect some surprises!
5.Analysis in operation S. Pejovic ‹#›
50% + hydroelectric plants & hydraulic systems of nuclear and other plants have troubles and accidents
Conclusions
IEEE Conferences, Montreal 2007 / 2009
We need Institution to teach experts!
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Prof. Stanislav Pejovic, Ph.D., P.Eng.. Website: www.StanPejovic.com
Email: [email protected]
The End
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Appendix
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Transient flow in close conditions is represented by equations of motion and continuity
02
cc
Dt
c
x
cc
x
hg
0
2
x
zc
x
c
g
a
x
hc
t
h
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This set of equations better suit for numerical integration
There are two sets of lines in the x-t plane, called
characteristic lines, defined by
acdt
dx
0sin2
a
gcc
Ddt
dc
dt
dH
a
g
Along these lines previous equations become
ordinary differential equations
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Pump-turbine dynamic equation of rotation
ao = f(t)
gloss
g
E
Pe P
PLimM
E
0
0
0
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“S” instability HDm
dt
dnJ 4'
1
'
1
30
HDmdt
dnJ 4'
1
'
1
30
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