FRANCIS TURBINES 1
The Francis turbine's operating range, whilst being midway between that of the Pelton and Axial Flow/Kaplan turbines, overlaps these turbines' operating domains.
The Pelton turbine, particularly in its multi-jet form, is competitive at higher heads, and the Kaplan and double regulated Axial Flow turbines, with their reasonably flat efficiency versus flow curves are more cost effective at lower heads.
The Francis turbine, however, is also very competitive - particularly as improvements in turbine and water passage design have reduced the hydraulic losses of this type of system.
The
Francis
turbines are manufactured in three configurations, these being:-
an open flume setting for low head sites
a concentric cased economy version for medium head sites
a spiral cased version for medium to high head sites.
The runners themselves are designed for low, medium or high speed operation and are specified to suit site conditions.