Quantitative operating risk assessment of Francis turbine unit under variable load in hydro-wind-solar complementary energy system

The hydro-wind-solar multi-energy complementary clean energy base (HWS-MECB) is an effective approach for renewable energy integration, in which hydro turbine unit (HTU) play a critical stabilizing role. However, participation in such systems forces HTUs to operate frequently in part-load regions with strong vibrations, increasing the risk of runner damage and unit failure. In this study, a Francis HTU with runner damage operating in the HWS-MECB at a hydropower station in northwest China is selected as the research object, and runner optimization is performed. A quantitative operating risk assessment method for HTUs is proposed by integrating principal component analysis (PCA) with the technique for order preference by similarity to an ideal solution (TOPSIS). Based on variable-load experimental data before and after runner optimization, the operating risks of the unit over full load range are quantitatively evaluated from mechanical and hydraulic perspectives. The results show that the proposed runner optimization significantly reduces operating risks by effectively suppressing shaft runout, vibration and pressure pulsation at critical locations. Compared with the condition before optimization, the mechanical risk coefficient is reduced by an average of 31.01% over the full load range. In the unstable operating region corresponding to 40%–50% of the rated power, the hydraulic risk coefficient achieves a maximum reduction exceeding 35%. After integration into HWS-MECB and long-term operation, ultrasonic inspections reveal no crack initiation or propagation in previously damaged runner regions. These results demonstrate the effectiveness of the optimized runner design and confirm the reliability of the proposed PCA–TOPSIS-based operating risk assessment framework.