Air pressure drop in a penstock during the course of intake-gate closure.

In urgent situations, the intake gates of a hydroelectric power generating station must be closed to stop the inflow of water to the station's penstock. During the course of gate closure, the air pressure in the penstock can drop drastically, posing safety risks. This paper aims to develop reliable methods for predicting pressure drop. The methods consider time-dependent water inflow, air entrainment in the penstock, air-water outflow from the penstock, and airflow down the air vent system. The methods are used to calculate time-dependent flow and pressure drop for two stations in Quebec, producing results in good comparison with field measurements. In the penstock, water jet intensifies in the first half of the closure time period, whereas air pressure drops in the last one third of the time period. Air entrainment is an important cause of pressure drop. The methods are useful for planning air-vent upgrades and safe closure operations. [ABSTRACT FROM AUTHOR]