Cavitation Erosion in Hydroturbines

This paper is based on a field survey of the operational and design characteristics of 729 hydroturbines installed since 1950 having either a capacity in excess of 20 MW or a discharge diameter greater than 3 m. This data base includes 67% of the total U.S. hydropower capacity (40,000 MW). A nondimensional erosion rate parameter is developed to make meaningful comparison of observed cavitation erosion rate with theory and laboratory experiments. Overall design parameters such as specific speed and unit speed for a given head are found to have little variation from manufacturer to manufacturer. However, cavitation erosion rate varies widely even when relative comparisons are made. These variations are attributable to variations in setting, manufacturing tolerances, and operational history of a given unit. Size effects appear more pronounced than predicted. Direct repair costs are only about 1.5 cents per megawatt hour, but hidden costs associated with reductions in useful life or degradation of efficiency or energy production losses could be very significant.