Stability analysis of hydro-turbine governing system with sloping ceiling tailrace tunnel and upstream surge tank considering nonlinear hydro-turbine characteristics

This paper aims to investigate the stability of hydro-turbine governing system (HTGS) with sloping ceiling tailrace tunnel (SCTT) and upstream surge tank (UST) considering nonlinear hydro-turbine characteristics (NHTCs). Firstly, the mathematical model of HTGS is presented based on nonlinear seventh-order state equation, which is verified by example analysis so as to study the stability of HTGS. Subsequently, the effect of HTGS parameters on the stability of the system is investigated with numerical simulation. Finally, the coupling effect mechanism of SCTT and UST on stability under the effect of NHTCs is revealed by using contrastive analysis. The results are summarized as follows: (1) Ta, Kd and Twt perform larger effect on the stability of HTGS, while the influence of F and Twy is mild; (2) the NHTCs are beneficial under negative load disturbance and unfavorable under positive load disturbance for the stability and dynamic performance of HTGS; (3) the coupling effect of SCTT and UST outperforms the results of SCTT or UST alone under all load disturbances; (4) the incorporation of UST to the established model plays a certain role in stability compensation, while the introduction of SCTT not only improves the stability but also achieves smaller amplitude and lower frequency.

Automated summary

This paper investigates the stability of hydro-turbine governing system (HTGS) with sloping ceiling tailrace tunnel (SCTT) and upstream surge tank (UST) considering nonlinear hydro-turbine characteristics (NHTCs). Firstly, a mathematical model based on a nonlinear seventh-order state equation is presented and verified by example analysis. Subsequently, the effect of HTGS parameters on the stability of the system is investigated through numerical simulation. Lastly, the coupling effect mechanism of SCTT and UST on stability under the effect of NHTCs is revealed by contrastive analysis. The results indicate that Ta, Kd, and Twt have a significant impact on the stability of HTGS, while F and Twy have a mild influence. The NHTCs are beneficial for stability under negative load disturbance but unfavorable under positive load disturbance. The coupling effect of SCTT and UST outperforms using SCTT or UST alone, and the introduction of SCTT improves stability and achieves smaller amplitude and lower frequency.