Specific speed effect on Francis runner reliability under various operating conditions

Energy market deregulation and the arrival of new forms of renewable energy, such as solar and wind powerplants, has led to an increasing demand for flexible operation of hydraulic turbines. Instead of continuous close to peak operation, it is nowadays not uncommon to see turbines being operated over the whole range, with many start/stops, extensive low-load operation, synchronous condenser mode and power/frequency regulation. This can affect the life expectancy of machinery as a result of the increased number of high and low amplitude cycles introduced in the operation of the units. It therefore becomes critical for the owner to understand the real effects of these dynamic phenomena. This paper shows how dynamic phenomena occurring at various operating conditions can affect the life expectancy of various specific speed Francis runners, and demonstrates how the relative importance of the dynamic hydraulic phenomena occurring in the runners may vary with specific speed.