Pressure measurements on a high-head Francis turbine during load acceptance and rejection

Hydraulic turbines are frequently used to maintain electrical grid parameters. An angular movement of the guide vanes (GVs) during transients such as load acceptance and rejection within short time raised significant concerns for increased wear and instabilities. The present work focuses on the pressure variations in a high-head Francis turbine during the transients. Six transient conditions were investigated including time-domain rotor-stator interaction. The measurements in the vaneless space and runner indicated the presence of unsteady vortical flow during transients. The vortices travelled to the runner and affected the flow in the blade channels. The GVs angular movement increases the pressure difference between the pressure and suction sides of the blade. The largest pressure variation was observed during the partial load rejection at the trailing edge of the blade. Preliminary results indicated that an appropriate closure of the GVs may minimize large pressure fluctuations in the runner.