5. Axial-flow turbines or bulb assemblies

5.1 General structure

A bulb turbine consists essentially of an axial turbine (the flow being axial) from the inlet section to the outlet section, directly driving an alternator operating inside a sealed, bulb-shaped housing. The assembly, with its horizontal or slightly inclined axis, is immersed in a gallery linking the upstream and downstream reaches of the hydroelectric scheme through the retaining dam (figure 29 ).

This layout is particularly well suited to very low heads (2 to 15 m), large tidal ranges and high flows (up to 400 m ³ /s). In this field, the bulb has practically supplanted the Kaplan...