Review of hydrodynamics instabilities in Francis turbine during off-design and transient operations

Electricity generation from solar and wind has raised a significant concern about the stability of grid networks. Hydroelectricity plays an important role to balance the stability of grid network. In order to improve the stability of presently high loaded grids, hydropower plants are being operated over a wide range of operations and experiencing frequent start-stop, load variation, and emergency shutdown. The power generating unit including turbine needs to sustain sudden change in its operating condition to balance the grid frequency. The objective of this paper is to present the operating problems of Francis turbine in the present energy generation scenario. The turbine suffers from several dynamic instabilities during off-design and transient operations. Several low and high-frequency pressure fluctuations are observed during both, steady state and transient operating conditions. The off-design operations such as part load and high load cause pressure fluctuations due to RSI, RVR and cavitation. The transient operations lead to heavy cyclic loading of its moving and stationary parts. Francis turbine also experiences asymmetric loading on the runner, cyclic stress, wear and tear; all of which reduce operating life of the components. Sometimes these rapid transient may cause failure of the unit and decouple it from the system.