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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 14 Steam leakage losses for a reaction stage design.<br />

stationary and rotating rows <strong>of</strong> a low-reaction stage will be higher than on a<br />

conventional reaction stage. Impulse-style blading has increased base<br />

section reactions to prevent the reentry <strong>of</strong> leakage steam between the<br />

stationary and rotating blades <strong>of</strong> a stage. Typical stage reactions at the mean<br />

diameter <strong>of</strong> low-reaction blading in intermediate-pressure turbines are about<br />

30 to 35%.<br />

Surface roughening occurs as a result <strong>of</strong> (1) deposits, (2) solid particle<br />

erosion, and (3) steam path damage such as weld beads, tools, thick<br />

deposits, and surface finish losses. The calculated percent change in turbine<br />

efficiency by stage as afunction <strong>of</strong> surface finish is shown in Fig. 15.<br />

Turbine Stage Losses<br />

The primary contribution to the overall turbine generator efficiency is the<br />

efficiencies <strong>of</strong> the individual turbine stages. The ideal stage efficiency is the<br />

Copyright © 2003 Marcel Dekker, Inc.

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