Investigation of Valve-Closing Law on the Maximum Head Rise of a Hydropower Plant

Piping systems commonly experience the transient-state situation as the result of changes to 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 e ects of di erent valve-closing laws on the maximum head rise at the end of the pressure shaft and other components are also investigated. Keywords: Method of characteristics; Hydropower plant; Transient ow; Valve-closing law; Karun 4 hydropower plant.