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Transient phenomenon with practical solution

dipl. ing. Aleksander Žagar mag. Miha Pišljar

www.turboinstitut.si info@turboinstitut.si

Turboinštitut d.d. Rovšnikova 7 1210 Ljubljana, Slovenija

Telefon: (01) 582 01 11 Telefax: (01) 582 01 12


Transient phenomenon

o Transient phenomenon o Mitigating water hammer o Solving practical problem o Computer program o Results of calculations o Conclusions June 2008


Transient phenomenon

Transient phenomenon and water hammer EMERGENCY STOP

pressure rise

PEN STOCK Determine possibility of water hammer: • Analytic methods • Numerical methods

June 2008


Transient phenomenon

Mitigating water hammer higher generator’s speed – run away

- Low fluid velocities - Slow closing guide vanes or valves

- Flywheel on generator or turbine shaft. - Hydro power bypass - Surge tank or pressure accumulators

surge tank

biger penstock higher price bypass

June 2008


Transient phenomenon

Solving practical problem 1. Bay pass valve to assure continuous flow of water at emergency shutting downs (price, place) Tehnical data :

river Sava

dam

forebay

penstock in tunnel

water bridge

Penstock is 600 m long with diameter 2,6 m

penstock

Nominal speed 600 min-1 Gross head 27.35 m Net head 24.5 m Nominal Unit flow 6,0 m3/s Turbine power 1300 kW Runner diameter 1000 mm Rotating inertial moment 5692 kgm2

Over pressure limit in penstock 150% Over speed limit 170%

power house

2. Relatively slow closing time and big flywheel

June 2008


Transient phenomenon

Computer program Transient behaviors of SHPP was studied on base of WCF program. Many commercial and non commercial packages exist today the following features should be considered when choosing the program: • wave speed variation • multiphase flow capabilities • an algorithm for cavitation growth and collapse • unsteady friction • varying bulk modulus for higher pressures (water will become less compressible) • fluid structure interaction • turbine characteristic shell diagram increasing turbine speed decrease flow turbine it self is causing water hammer effect

June 2008


Transient phenomenon

Calculations ‘’for turbine by it self causing water hammer effect’’

Time, s

Time, s

June 2008


Transient phenomenon

Results of final calculations for project Sava

Time, s

Time, s

June 2008


Transient phenomenon

Results of final calculations for project Sava

Time, s

Time, s

With variation of distributor‘s closing time and variation of flywheel optimal solution was determined.

June 2008


Transient phenomenon

Conclusions  During design stage all possible worst cases should be investigated.  Simplification can be done only with a lot of knowledge  Exact calculation, experimentally proofed, can be perfect background for simplified solutions to achieve:

 cheaper  reliable  simpler to maintain  safe  environment friendly

June 2008


Thank you for your attention Aleksander-Sašo Žagar


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