Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . w reaction turbine (Fig. 102, page 210,and Fig. H2i), represent the machines best suited for averageoperating conditions. In most cases the former would be pre- COMMERCIAL TYPES 227 ferred; but when the speed is to be made particularly low thepreference goes to the latter. Thus with a speed of 3600 driving a 60-cycle generatorat, say, 500 kilowatts, the best design would be a combinedimpulse and reaction machine for best efficiency and lowestcost. If, however, the
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . w reaction turbine (Fig. 102, page 210,and Fig. H2i), represent the machines best suited for averageoperating conditions. In most cases the former would be pre- COMMERCIAL TYPES 227 ferred; but when the speed is to be made particularly low thepreference goes to the latter. Thus with a speed of 3600 driving a 60-cycle generatorat, say, 500 kilowatts, the best design would be a combinedimpulse and reaction machine for best efficiency and lowestcost. If, however, the generator to be driven was for 25-cyclesendee, with an allowable maximum speed of 1500 andthe same capacity the single-flow reaction turbine would beselected, providing reaction blading was to be used at all. In general, however, the application of the combined impulseand reaction turbine, consisting of an impulse element for thehigh-pressure portion and reaction blading for the low-pressureportion, is well adapted for complete expansion turbines overwide ranges of power and speed; and since the introduction of. Fig. 112E. Relative Lengths of Rotors in Two Common Types. this type, a large proportion of the firms building steam turbineshave utilized this construction, either with Parsons or Rateaublading following the Curtis impulse element in the high-pressure end. The principal advantage of this type of con-struction is the shortening of the machine without very muchloss in efficiency, the elimination of balancing pistons with theavoidance of the very considerable leakage of steam throughthem, and the securing of high economies at light loads by theapplication of the method of governing by cutting out nozzles(see page 277), now applied to Westinghouse turbines of thecombined impulse and reaction type. 228 THE STEAM TURBINE Fig. ii2h shows the relative lengths of the rotors of the latestdesign of Westinghouse turbine with combined impulse bladingand single-flow reaction
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