On the pump mode shutdown sequence for a model contra-rotating pump-turbine

Paper in proceeding, 2025

Contra-rotating pump-turbines are currently being studied in the ALPHEUS EU H2020 project as an alternative for low-head pumped hydro storage (PHS). To have an efficient PHS facility, it is important to know how to operate the pump-turbine unit under transient conditions to be able to adapt to demand variations rapidly. Therefore, this study focuses on the transient pump mode shutdown sequence of a contra-rotating pump-turbine. Two different sequences are evaluated using computational fluid dynamics simulations. The sequences are denoted as ‘preliminary’ and ‘new’ since the preliminary sequence is similar to a sequence in one of our earlier studies. It is shown that the preliminary sequence produces reverse flow and large load gradients on the runners. The new sequence manages to avoid reverse flow and reduces the load gradients. The main reason the new sequence is advantageous is because a valve is closed before speeding down the runners. However, the new sequence produces larger load fluctuations, and a wider frequency spectrum of pressure fluctuations, compared to the preliminary sequence.