. Electric railway journal . Throughout the entire turbine,with the exception of the last few stages, steam speeds onlyabout 25 per cent in excess of the corresponding bladespeeds are employed in order to secure maximum efficiency. 924 Electric Eailway Journal Vol. 54, No. 20 In the last stages the steam speed may be twice the bladespeed. When the height of a row of blades is fixed, the area of thesteam space is dependent upon the angle formed betweenthe center line of the row of blades and the outlet portionof the blade. The smaller this angle is, the smaller will bethe area and vice versa; o
. Electric railway journal . Throughout the entire turbine,with the exception of the last few stages, steam speeds onlyabout 25 per cent in excess of the corresponding bladespeeds are employed in order to secure maximum efficiency. 924 Electric Eailway Journal Vol. 54, No. 20 In the last stages the steam speed may be twice the bladespeed. When the height of a row of blades is fixed, the area of thesteam space is dependent upon the angle formed betweenthe center line of the row of blades and the outlet portionof the blade. The smaller this angle is, the smaller will bethe area and vice versa; on the other hand, the smaller theangle the higher the efficiency, because of the lower absolutevelocity left in the steam discharged to the condenser. Chief among the physical factors limiting turbinecapacity are the physical characteristics of the materialsemployed and the chosen limits to which these materialsmay safely be stressed. Conservatism demands adherenceto the lower-strength, less-sensitive materials, rather than. ^0000 2Z000 24000 26000 2BOO0 JOOOO 31000 34000 36000Shift Load CHARACTERISTIC CURVES OF LAST STAGE OF 21,00O KW. TURBINE special alloy steels; and such materials may, with suitableforms of construction, be safely stressed under the maxi-mum stress condition to within a few thousand pounds oftheir true elastic limits. The steel regularly used by theWestinghouse company for turbine rotors shows these char-acteristics with standard 2-in. specimens: Tensile strength65,000 to 75,000 lb. per square inch; true elastic limit22,000 to 25,000 lb.; elongation 15 to 18 per cent, and re-duction of area 20 to 25 per cent. The material is obtainedordinarily in the form of castings, although occasionallyforgings are used. There exist two interesting relations between the stressat the base of the blade, the steam passage area through theblade and the rotative speed. They are these: (1) Forany given rotative speed and blade angle, the steam capacityor steam area through the
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