OTHER COMPONENTS OF HYDROPOWER PLANTS 521
12.9.3 Turbine governorsThe governor is a mechanism controlling the rotational speed of the turbo-
generator unit; constant speed must be maintained in order to obtain the
a.c. supply with constant frequency. As the turbine and hence its intercon-
nected generator tend to decrease or increase speed as the load varies, the
maintenance of an almost constant speed requires regulation of the
amount of water allowed to flow through the turbine by closing or opening
the gates (or nozzles) of the turbine automatically, through the action of a
governor. A simple governing mechanism for turbines is shown in
Fig. 12.19. Increase in the rotor speed raises piston A, permitting oil to
enter chamber B, thus closing the gates slightly. The operation is reversed
if the speed drops.
Fig. 12.19 Turbine governors