Research on start-up strategy of mixed-flow pumps in pumped storage systems: Quantitative assessment and optimal mode acquisition

In pumped storage systems, mixed-flow pumps (MFPs) are frequently subjected to start-up and shutdown operations to meet grid regulation demands driven by the variability of renewable energy sources. The start-up strategy (SUS) significantly affects the transient hydraulic stability of MFPs during the start-up process (SUP). Based on stability experimental data, this research quantitatively analyzed the effect of different power exponential law (PEL) SUSes on the stability of MFP by signal analysis method and technique for order preference by similarity to ideal solution (TOPSIS) method. The results indicate that the power exponent (PE) of PEL SUSes significantly affects the stability of MFP during the SUP. The increase in PE helps to reduce the shock shaft vibration (SV) and the pressure pulsation (PP) amplitude in the pump during the SUP. Moreover, it can also lower the total effective sound pressure level (SPL) of the MFP in the SUP. By comparing the stability index (St) that integrate the characteristic values of multi-source signals, the stability of the MFP started in Strategy 5 (PE is 4) is 62.66 % lower than that in Strategy 3 (Linear). The nonlinear polynomial fitting method is employed to establish the relationship between the PE of SUSes and the St. And then the PE with the optimal St is established to be 3.65, corresponding to the Strategy-P3.65. Experiments have confirmed that Strategy-P3.65 outperforms the other five strategies in terms of SV, noise and PP, verifying the reliability of the fitted model.