Effect of transients on Francis turbine runner life: a review

The present electricity market and the injection of power generated using intermittent energy sources have brought instability in the operation of the power grid. This has resulted in frequent load variations, emergency shut-down and restart, total load rejections, and off-design operation of grid connected hydraulic turbines. The present paper reviews the available literature summarizing the effects of transients on Francis turbine investigated experimentally, numerically, and analytically. Transients create both steady and unsteady pressure loading on the runner blade, resulting in cyclic stresses and fatigue development in the runner. These effects shorten the runner life, increase cost of plant operation, and loss of power generation. The reviewed literature has shown that one startstop cycle can shorten predefined refurbishment time up to 15hours. Turbine startstop cannot be avoided, but runner life may be improved by minimizing the unfavourable pressure loading on the blades during transients through strategic movement of guide vanes.