In transient conditions, the machines behave in a way different from steady-state operation. Compared to grid operation, components may suffer much higher alternating loads, this holds in particular for start-up and quick shutdown manoeuvres.
Today many hydro plants are expected to play a more active role in network regulation; this may also imply more frequently starting and stopping the units. Transient manoeuvres thus become more important for the service life of important components. While it was formerly OK to select the parameters of a starting procedure for fast and reliable synchronization only, the aspect of mechanical fatigue will have to be given more attention in the future.