Hydroturbine Cavitation Erosion

Abstract

This paper is based on an analysis of turbine cavitation data obtained from 729 turbines installed in the United States since 1950 and 19 selected Canadian turbines. An equation has been developed to express the anticipated rate of cavitation within 75% and 95% confidence limits. The equation is a function of the turbine setting with respect to tailwater, the runner throat velocity, the number of runner blades, the barometric pressure at tailwater less water‐vapor pressure, the runner material, the hours of operation, and the plant‐use factor. The equation can be used to: (1) Select an appropriate setting level for the turbine with respect to tailwater; (2) determine the maximum capacity of a new runner to be installed in an existing casing; and (3) determine the rate of erosion due to cavitation. A preliminary equation also has been developed for estimating the expected efficiency of a new runner in an existing casing, which is a function of the type of casing and draft tube, the number of runner blades, the net head, and the runner throat velocity. Examples of equation use are provided.