Experimental investigations of a model Francis turbine during shutdown at synchronous speed

Hydraulic turbines are widely used to meet the real-time electricity demand at moderate to low cost. Intermittency in the power grid due to high penetration of wind and solar power has raised significant concerns for grid stability and reliability. The intermittency results in an increase of the start–stop cycles of hydraulic turbines. Each cycle induces fatigue to the turbine runner because it experiences unsteady pressure loading of high amplitude. The turbine runner accelerates freely due to an instantaneous transition into no load during shutdown. The amplitude of the unsteady pressure pulsation increases as the runner accelerates. To investigate the unsteady pressure pulsation, a shutdown slightly different from the normal shutdown was performed. Guide vanes were closed completely before the generator was disconnected from the load. The runner was spinning at constant angular speed through the generator. Amplitudes of the pressure pulsations were 20% and 35% lower in the vaneless space and the runner, respectively, compared to the normal shutdown of the turbine.