Abstract
The purpose of this paper is to illustrate a new method whereby the most efficient and also the most economical proportions of a draft tube for a water-turbine installation may be found. A study is made of the excavation and concrete costs, as the ratios of draft-tube width to runner diameter and draft-tube depth to runner diameter increase. These costs are compared to the actual capitalized value of the horsepower saved due to the increased efficiency, as either ratio is increased. The comparison is made by means of computed curves and includes the ordinary range of power costs, as well as a range of load factors from 50 to 100 per cent, at which the unit might be expected to operate. The paper develops a method to overcome the seemingly prevalent practice of many turbine manufacturers of installing a certain definite size and shape of draft tube with a certain size runner without regard to the various factors which should enter into the selection.