Department of Mechanical Engineering,Sharif University of Technology
Abstract. Piping systems commonly experience the transient-state situation as the result of changes
ow conditions during pump failures, valve closures or turbine load rejection. This paper addresses
transients as a consequence of the load rejection of a Francis hydropower plant (Karun 4, Ahwaz, Iran).
To control the turbine system and related equipment during load rejection, the valve closing law of wicket
gates is of paramount importance. The pressure rise at the end of the pressure shaft, the pressure drop in
the draft tube and the speed rise while the electromagnetic braking torque disappears are solely dependent
on the closing curve. Thus, an optimum closing law can eliminate the probable risk of damage to the
units. This paper develops a computational model to calculate water-hammer system components, such
as pressure rise, speed rise, discharge variations and pressure
uctuations. Results obtained from the
present model are compared and validated with those obtained by a consultant at the Karun project. The
eects of dierent valve-closing laws on the maximum head rise at the end of the pressure shaft and other
components are also investigated.