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