Analysis of Pump-Turbine S Instability and Reverse WG Bgd Oct 2011 Pejovic BG KZ AG Keynote... ·...

6/4/2010

Analysis of Pump-Turbine “S” Instability and Reverse Waterhammer Incidents in Hydropower Systems

Stanislav Pejovic pejovics@asme.org, 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

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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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32

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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34

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: pejovis@asme.org

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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