Experimental Investigation of the Fatigue-Induced Damage in Hydroelectric Units During Start-Up

In view of a global trend towards an increasing share of renewable energy sources, improved flexibility of operation is needed in pumped storage power plants (PSPPs) to support this transition. The repeated changes in PSPP operation to balance the grid have a significant impact on the unit’s lifespan and could be mitigated thanks to variable speed unit. This study proposes a method to quantify the impact on the impeller lifespan of various start-up procedures that take advantage of the variable speed to decrease the amount of damage induced to the impeller. An experimental campaign has been performed on a Francis-type reversible pump-turbine reduced-scale model equipped with strain gauges and pressure sensors. This test provides the measurement of the stresses that blades experience during a given start-up sequence and provides a framework to evaluate various sequences for damage comparison, providing a quantification on remaining lifespan of the unit. In this respect, the detailed study of pressure fluctuations is facilitated by employing the Continuous Wavelet Transform, providing insight on the underlying phenomena occurring throughout a start-up procedure. The results of the study show a significant reduction in the damage production for sequences using the speed control capability offered by variable speed unit.