Archimedean screws which were driven by windmills. In modem installations, however, the pumps are invariably of the centrifugal type, driven by a steam, gas, or electric motor.
Performance of 3o,ooo-Kw. Steam Turbo-generators. ANON. (Electrical l.[/orld, vol. 67, No,. 2o, May 13, 1916.)--The extent to which the steam turbine has displaced the piston engine in large units is strikingly shown by the performance of the 3o,0oo-Kw. units recently installed in the Seventy-second Street Station of the Interborough Rapid Transit Company of New York. In 19oo this station housed eight Reynolds Allis-Chalmers steam engines of a double combination horizontal-vertical cross-compound design. Each unit was rated at 5ooo Kw., with a maximum rating of 75oo Kw. In a space no greater than taken by one of these units a 3o,ooo-Kw. turbine unit now stands, operated from the same boilers now equipped with underfeed stokers, and superheaters to give 2o0 degrees of superheat when the boilers are delivering three times their rated output. The boiler pressure is 2o 5 pounds per square inch gauge. The steam engines operated originally at 175 pounds gauge and no superheat. The cost of the engines, generators, and condensers was $4o per kilowatt, while the cost of the new turbine and condensers is $9 per kilowatt. The steam engine water rate was 17 pounds per kilowatt-hour, as compared with about i 1.4 for the turbines operating under similar load conditions.
The performance of the unit in outclassing in operating efficiency, cost, space requirements, and ability to handle swinging loads amply establishes the enviable position of the steam turbine as a prime mover. The old engines, which at the time of their installation represented the last word in engine design, found no purchaser but the junk dealer. It is also interesting to note that, although it was decided two years ago to use this new type of turbine, changes in the art and operation in the interim have been such that the company will now install a 7o,0oo-Kw. cross-compound unit with three generators, any one of which may be operated independently if desired. Thus this art of generating electricity in steam-turbine driven stations has advanced to a point where, up to load factors of approximately 6o per cent., a kilowatt-hour of electrical energy can be manufactured more cheaply by this means than by water power.