WATER HAMMER CONTROL ANALYSIS IN KAPLAN TURBINE HYDROELECTRIC POWER PLANT Case of HPP Blanca, Slovenia Jernej Mazij, Litostroj Power d.o.o. CIGRE 2011 Pržno, 16. – 19. 05. 2011

Content • Water hammer control • Computational method • Numerical and field test results • Conclusions

Water hammer control (1) Alteration of operational regimes Regulation of the wicket gate and runner blade manoeuvres. (2) Installation of surge control devices in the system Increased turbine unit inertia, surge tank, air cushion surge chamber, pressure-regulating valve, pressure-relief valve, rupture disc, aeration pipe, air valve. (3) Redesign of the flow-passage system layout Conduit profile and dimensions, position of system components.

Computational method 1) Elastic water hammer theory Transmission of pressure waves. (2) Rigid water hammer theory Incompressible liquid and rigid pipe walls. Rigid water hammer is described by the one-dimensional Bernoulli equation for unsteady flow which is solved simultaneously with the dynamic equation of the turbine unit rotating masses, taking into account the turbine characteristics.

Computational method Criteria for potential danger of full water column separation under the turbine head cover (1) Turbine head cover pressure criterion The computed absolute pressure should be larger than the vapour pressure. (2) Axial hydraulic thrust criterion The maximum negative axial hydraulic thrust shall be less than the total weight of rotating parts of the unit and the damaging axial hydraulic thrust acting upwards.

Computational method Axial hydraulic thrust criterion Maximum permissible axial hydraulic thrust acting in the negative direction: The damaging axial hydraulic thrust acting upwards:

Numerical and Field Test Results Layout of the HPP Blanc with turbine runner diameter D = 5,0 m

Numerical and Field Test Results Rigid water hammer analysis I (1) Normal operating regimes - turbine start-up - load acceptance - load reduction - normal shut-down of the unit - load rejection under governor control - mechanical quick-stop - emergency shut-down

Numerical and Field Test Results Rigid water hammer analysis II (2) Emergency operating regimes - partial turbine runaway - emergency shut-down with inoperative runner blades (3) Catastrophic operating regimes - turbine runaway (on-cam) - maximum turbine runaway (off-cam)

Numerical and Field Test Results Prototype measurements - turbine start-up - testing of the turbine speed sensing device - load acceptance - load reduction - load rejection under governor control - mechanical quick-stop - electrical emergency shut-down - testing of auxiliary governor hydraulic system

Numerical and Field Test Results Load rejection under governor control (P = 10,5 MW)

Numerical and Field Test Results Emergency shut-down (P = 16,6 MW)

Conclusions (1) The rigid water hammer theory can be used for plants with relatively short inlet and outlet conduits. (2) Water column separation under the turbine head cover can be indicated by the axial hydraulic thrust criterion.

Conclusions (3) There is a reasonable agreement between the computed and measured magnitudes of the scroll case pressure head, turbine rotational speed and negative axial hydraulic thrust. (4) Larger discrepancies between the com- puted and measured traces of the turbine rotational speed and axial hydraulic thrust occur at small wicket gate openings.