Present Limits of Speed and Power of Single Shaft Curtis Steam Turbines

This paper starts by showing that the limit of a single-unit turbo generator does not lie in the generator but is confined to the steam turbine, and that the last wheel of the turbine is the limiting feature. The author therefore takes the last wheel of an 1800-rev. per min. turbine, giving dimension stresses, kind of material used etc., and then designs two turbines, one having 23 stages and the other 13 stages, both machines using this last wheel, and shows that a turbine can be built having its most economical point at 21,000 kw., under steam conditions given in the paper. Under this condition the last stage absorbs 11.5 per cent of the total adiabatic available energy, and the wheel efficiency is 66.25 per cent. As the load increases, the work done in this stage also increases, so that at 36,000 kw. the energy is practically doubled, but with a sacrifice in efficiency of about 18 per cent, which naturally lowers the efficiency of the turbine as a whole. A 5000-kw., five-stage, 3600-rev. per mill. turbine load curve is also given and discussed, and the author claims that if the construction could be made similar to the large turbine, keeping the same stresses and number of stages, a turbine of this capacity could be built as efficient as the larger machine at 20,000-kw.