1. 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. –

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

3. 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.

4. 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.

5. 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.

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

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

8. 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

9. 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)

10. 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

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

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

13. 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.

14. 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.