Niagara Falls 100.000-Hp. Development

24 ] Niagara Falls 100,000 Hp. Development FIG. 32—ROTOR SPIDER AT FACTORY AND BEING ASSEMBLED WITH RIM. THRUST BEARING DURING ASSEMBLY AT RIGHT air into closed pressure chambers, from which air is forced into the air gap and between the field coils and through radial ducts in the armature core. Air enters the generator from both top and bottom. The generator frame is surrounded by a circular sheet steel casing in which all of the warm air from the generator is col- lected and discharged outdoors. There are twenty thermocouples located between coil sides in the armature slots and six couples on the out- side of the armature coil ends. These latter couples were installed to duplicate mercury thermometer measurements as ordinarily taken on smaller open-type generators and for comparative purposes only. The couples built in the core are well protected from pos- sible air currents where the armature vent ducts cross the slots and should give indications reasonably close to the actual temperature of the copper inside the insula- tion. At 28,500 kw., 90 per cent power factor and 13,000 volts the highest reading thermocouple within the core gave a rise of 56 deg. C. and the highest reading couple FIG. 33—SECTION OF ARMATURE SLOT AND FIELD COIL Armature strands are of different size and complete insulation is provided when only two strands are insulated. on the outside of the coil ends showed a rise of only 23 deg. C. This, as stated before, is equivalent to the ther- mometer measurement formerly used and for which a temperature guarantee of 50 deg. rise was standard practice. Operating Experience Proves Correctness of Design of 32,500-Kva. Generator By R. B. Williamson Engineer in charge of Alternating-Current design, Allis- Chalmers Manufacturing Company THE 32,500-kva. generating unit built for the Ni- agara Falls Power Company by the Allis-Chalmers Manufacturing Company is mounted directly above a 37,500-hp. turbine, the two forming a close-coupled unit with a relatively short distance between the two ma- chines. The generator of this unit was described by the writer in the Electrical World, Aug. 30, 1919, before it was put into service, but further information is now available as a result of several months of operation. The shaft is short and stiff and the combined unit has but two guide bearings, one at the top of the generator immediately below the thrust bearing and the other directly above the waterwheel runner. To carry the generator a large cast-iron barrel of heavy- ribbed design is bolted to the cast-steel speed ring of the turbine, thereby transmitting the weight of the generator through the barrel to the speed ring and foundation below the wheel. With these large vertical units it is necessary to pro- vide brakes for bringing the machine to rest and for holding it in case of leakage through the wheel. In this instance the brakes are operated by air pressure and engage the lower surface of the field spider rim. On account of the large size of the generator it was considered advisable to stack the laminations and put the stator coils in place in the field after the stator yoke had been set on the pit liner connecting the gen- erator and turbine as shown in the illustration above..