The gross efficiency of the whole arrangement of turbine, races, and transmissive machinery is
ηt = Td / CQHt.
(6)
And the hydraulic efficiency of the turbine alone is
η = T / GQH.
(7)
It is this last efficiency only with which the theory of turbines is concerned.
From equations (5) and (7) we get
ηGQH = (GQ/g) (w1r1 − w2r2) α;
η = (w1r1 − w2r2) α/gH.