Niagara Falls 100.000-Hp. Development

Niagara Falls 100,000 Hp. Development [25 IN TWO DESIGNS OF GENERATORS The temperature rise guaranteed on the generator was 55 deg. C. as indicated by resistance coils placed in the windings between the upper and lower coils in the middle of the stator core. Continuous operation at full load has shown the rise as thus indicated to be well within the allowable limit. The winding is equipped with twenty temperature indicating coils, and the rise as indicated by them is quite uniform throughout the machine. Measurements of the temperature rise and quantity of oil circulated through the thrust-bearing casing indicate that the friction loss in the bearing does not exceed 25 hp. or 0.066 per cent of the rated output. In the present design the coils are securely blocked just where they project beyond the core to protect them against any side motion and consequent danger of breaking the insulation at the ends of the slot. They are also lashed to the insulated supports, as indicated at the right in the accompanying sketch. These supports are made in sections and are bolted to projecting brack- ets cast on the stator end heads. As this generator requires approximately 80,000 cu.ft. (2,240 cu.m.) of air per minute for carrying off the heat, the arrangements for handling the air required careful consideration. Air is taken in at the top and also from the pit underneath and, after passing over the windings and through the stator yoke, it flows through ducts and is forced out of the station by means of auxiliary fans. This method was decided upon after careful consideration and conferences between the Niagara Falls Company engineers and the designers. Design of 32,500-Kva. Generator Is Conservative—* By W. J. Foster Designing engineer, General Electric Company CONSERVATISM has characterized practically every feature of the design of the generator built by the General Electric Company. The mechanical stresses allowed in the various parts, such as bearings, spider and rotor, are in many cases no higher than is some- times allowed when using cast iron, whereas the best steel is being used. Because of the high efficiency that has been striven for relatively small losses occur and the. insulation is not required to withstand abnormal temperatures. The guarantee to the customer is a 100-deg. C. machine at the rated output—32,500 kva. This is 5 deg. more conservative than the standard of the American Institute of Electrical Engineers for class A, or low-temperature, insulation, whereas the insula- tion that has been used in the armature for both turn and external insulation is class B. This insulation, ac- *Covered more completely in May 31, 1919 Electrical World. cording to A. I. E. E. standard, is suitable for 125 deg. In order to produce a simple and mechanically strong rotor the rotor spider was constructed of six wheels, each wheel a single casting of steel. The upper end of the shaft is machined for a thrust collar which takes the entire weight of rotating parts and for a guide bearing which is immediately below the thrust bearing. Only one other guide bearing is provided, and that is on the waterwheel. The reactance of the generator is approximately 20 per cent, which permits the stator winding to be sup- ported mechanically with unusually large factors of safety against the stresses produced by instantaneous short circuits. The projecting ends of the winding at both top and bottom rest back against two solid steel rings that are carried by brackets attached to the heads of the stator. These rings are heavily insulated to form a seat for the coils. The individual coils are laced to supporting bands by strong linen cord specially treated. The individual coils also have spacing blocks laced to their sides at short intervals, of such thickness as to make the completed winding perfectly ring-bound.