The type of turbine selected for a particular application is influenced by the head and flow rate. There are two classifications of hydraulic turbines: impulse and reaction.
The impulse turbine is used for high heads—approximately 300 m or greater. High-velocity jets of water strike spoon-shaped buckets on the runner which is at atmospheric pressure. Impulse turbines may be mounted horizontally or vertically and include perpendicular jets (known as a Pelton Jet type), diagonal jets (known as a Turgo Jettype), or cross-flow types.
In a reaction turbine, the water passes from a spiral casing through stationary radial guide vanes, through control gates and onto the runner blades at pressures above atmospheric. There are two categories of reaction turbine—Francis and propeller.
In the Francis turbine, installed at heads up to approximately 360 m, the water impacts the runner blades tangentially and exits axially. The propeller turbine uses a propeller-type runner and is used at low heads—below approximately 45 m.
The propeller runner may use fixed blades or variable pitch blades—known as a Kaplan or double regulated type—that allows control of the blade angle to maximize turbine efficiency at various hydraulic heads and generation levels.
Francis and propeller turbines may also be arranged in a slant, tubular, bulb, and rim generator configurations. Water discharged from the turbine is directed into a draft tube where it exits to a tailrace channel, lower reservoir, or directly to the river.
The impulse turbine is used for high heads—approximately 300 m or greater. High-velocity jets of water strike spoon-shaped buckets on the runner which is at atmospheric pressure. Impulse turbines may be mounted horizontally or vertically and include perpendicular jets (known as a Pelton Jet type), diagonal jets (known as a Turgo Jettype), or cross-flow types.
In a reaction turbine, the water passes from a spiral casing through stationary radial guide vanes, through control gates and onto the runner blades at pressures above atmospheric. There are two categories of reaction turbine—Francis and propeller.
In the Francis turbine, installed at heads up to approximately 360 m, the water impacts the runner blades tangentially and exits axially. The propeller turbine uses a propeller-type runner and is used at low heads—below approximately 45 m.
The propeller runner may use fixed blades or variable pitch blades—known as a Kaplan or double regulated type—that allows control of the blade angle to maximize turbine efficiency at various hydraulic heads and generation levels.
Francis and propeller turbines may also be arranged in a slant, tubular, bulb, and rim generator configurations. Water discharged from the turbine is directed into a draft tube where it exits to a tailrace channel, lower reservoir, or directly to the river.