Report Upon Efficiency Tests of a 60,000-Kw. Cross-Compound Triple-Cylinder Steam Turbine

Abstract

Abstract The present paper contains the results of tests on the 60,000-kw. Westinghouse turbine installed at the 74th Street power station of the Interborough Rapid Transit Company, New York City. This turbine is of the cross-compound, triple-cylinder type, consisting of one high-pressure element and two low-pressure elements, each element driving a separate generator. The normal steam pressure at the throttle is 220 lb. abs. with a superheat of 150 deg. fahr. exhausting into a vacuum of 29 in. Hg. The speed of all three elements is 1,500 r.p.m. The primary steam inlet takes care of all loads up to 40,000-kw. A secondary inlet which bypasses the first six stages cares for all loads up to 50,000-kw., after which a tertiary inlet which bypasses the first ten stages opens and increases the capacity to 60,000-kw. The generators are able to carry a maximum load of 70,000-kw. for two hours, this being effected through a hand-operated quaternary valve which bypasses four additional stages of the high-pressure turbine. The lowest water rate obtained while operating the complete unit under normal conditions was 11.00 lb. per kw-hr., while the highest Rankine and thermal efficiencies obtained were 76.0 per cent and 25.1 per cent., respectively. With the high-pressure and one low-pressure turbine in service the lowest water rate was 11.25 lb. per kw-hr. Results of tests of 30,000-kw. Westinghouse cross-compound turbines at the same station were presented before the Society in 1916 in a paper by H. G. Stott and W. S. Finlay, Jr., and of 30,000-kw. General Electric turbines of the straight Curtis impulse type in a paper read at the Spring Meeting, Chicago, May, 1921, by the senior author of the present paper.