Pumping Fluid Hydroturbines Hydropower is produced by damming a river to provide a reservoir of water at a level that is higher than that downstream.
Water is piped from the reservoir to a hydroturbine that discharges into the downstream flow.
Since river flow may exceed the hydroturbine capacity in some seasons of the year, a spillway is provided to bypass the hydroturbines whenever necessary. Hydroturbines ordinarily run at a fixed speed because they generate electricity of required frequency. The available head is nearly constant, although the reservoir level may change with the river flow. The power generated by the hydroturbine can be regulated by varying the flow rate through the turbine which is accomplished by adjusting the inflow passage area. The mechanical power of the hydroturbine must match the electrical power of the alternator it drives, which in turn is tied into an electric power distribution network.