Niagara Falls 100.000-Hp. Development

Niagara Falls 100,000 Hp. Development [21 as 0.2. This gave a transverse force of 104,000 lb. and a longitudinal force of 136,000 lb. applied at the top of the crane girder to be taken care of in addition to the regular maximum wheel loading of 76,000 lb. In the design of the steel work it was assumed that an equal portion of the lateral load would be taken by the top flange of each set of crane girders. The top flange of the crane girders was proportioned for the combined stresses due to the vertical and lateral forces, the span length in each case being the distance between the column centers. The columns and trusses were designed as a portal fixed at the base. The lateral reaction from the crane girder was assumed to be taken by both the crane col- umn and the truss column. The amount taken by each of these members was determined by the lateral deflec- tion in these members for their particular condition of loading. The longitudinal force from the crane was assumed to be taken by the crane column, knee braces and the crane girder. In determining the final sections the allowable unit stress in all members that were increased by the lateral or longitudinal forces due to the action of the crane were made 25 per cent greater than the allowable unit stress in the members not affected by this loading. ____________ Factors Determining the Design of Generators F^OR the extension to Station No. 3 the Niagara Falls Power Company placed orders for three generators with three different manufacturers. While about all that was specified was the high- est efficiency consistent with other desirable and impor- tant characteristics, such as reliability, no restrictions as to the kind of material or weights of parts were placed upon the designer. They are so nearly alike in external appearance, however, that they might well have been built from the same patetrns. These machines are rated at 32,500 kva., 12,000 volts and due to this size involved interesting problems of design. In the following articles features of design are given by the several designing engines. __________________________________________________ Reliability Is Keynote of Generator Problems Arising in the Selection of Number of Stator Slots, Provision for Insulation and Support of Coils and Thrust Bearing Design Are Discussed By F. D. Newbury Westing house Electric & Manufacturing Company THE 32,500-kva. generator built for the Niagara Falls Power Company by the Westinghouse Elec- tric & Manufacturing Company is notable chiefly for its size and for precautions taken in its design and con- struction to assure reliability and safety in operation. Owing to the rating of the unit (12,000 volts, 1565 amp., 25 cycles and 150 r.p.m.), certain details of design attracted particular attention, namely, the number of slots to use, armature-coil insulation for 12,000 volts, support of coil ends, rotor construction, field-coil insu- lation, bearing support, lubrication and ventilation. The factors which were taken into consideration in de- ciding on these details are discussed in the table below. Number of Armature Slots.—The number of armature slots is a detail that received considerable thought during the design. The choice was between 240 slots and 300 slots, the larger number being finally selected. The advantages of the smaller number of slots are greater ratio of copper to insulation space and a more rigid and stronger coil due to the greater ratio of coil width to coil depth. This is a matter of considerable importance in insulating long coils with mica. The important advantage of the larger number of slots, and the one that decided the selection, is the greater ratio of coil surface to copper loss and the resulting ability to transmit the heat developed in the copper through the insulation with a lower temperature drop. A 0.75- in. slot is narrower than is commonly used in a large 12,000-volt generator. The ratio of bare copper width to the punched size of the slot is, however, 0.44, which is good considering the high voltage and narrow slot and is possible largely because of the compact machine- wrapped coil insulation. The importance of a large ratio between armature coil surface and armature copper loss is sometimes overlooked. The problem of dissipating the armature copper loss is very largely a problem of heat-conduction through the armature-coil insulation. In high-voltage 25-cycle generators, having relatively low tooth losses and core temperatures, roughly two-thirds of the tem- perature rise of the copper is due to the temperature drop through the insulation and only one-third is due to the temperature rise of the armature teeth above the cooling air. It follows, therefore, that the factors affecting the dissipation of heat by ventilation are rela- tively only half as important as factors affecting the conduction of heat through the insulation. To illus- trate: Assume a total armature copper temperature rise of 60 deg., then 20 or 25 deg. would be the tem- ___________________________________________________ PKINCIPAL DIMENSIONSAND WEIGHTS OF 32,500-KVA., 12,000-VOLT, THREE-PHASE, 25-CYCLE, 150-R.P.M. WESTINGHOUSE GENERATOR ___________________________________________________ Stator Outside diameter of core............... Inside diameter of core......................... Core width (including 30—| in air ducts) Number armature slots.................. Dimensions of slots.................... Coils located in slots................. Armature winding................. Y Size of conductor strands............... Arrangement of conductors.............. Turns per phase in series.............. Development length — one turn.......... Rotor Outside diameter......................... Single air gap......................... Pole face.............................. Pole body.............................. Radial height of pole.................. Field winding............................ Developed length —one turn............... Amperes excitation no. load 12,000 volts. _____ ............. Amperes excitation 1,565 amp. 12,000 volts, 80 per cent P.F. ............................ 228 in. ............................ 197 in. .......................... 65 in. ........................... 300 .............75 x 4.75 (over all) .....__ 1 and 14 connected — 4 parallel circuits f . 204 x . 258 (mica taped) .....(.129 x .274 (bare) .................. See illustration ............................ 75 .......................... 257 in. .................. 196 in. .....>....... 0.5 in. .... 21 in. x 65 in. ..... 15 in. x 65 in. .....__....... 12f in. 42J turns per pole .203 x 2.25 bare strap 167 in. 323 ........ 632 Weights Total weight of generator............................... 650,000 pounds Total load on thrust bearing............................. 478,000 pounds Weight of generator rotor with shaft..................... 318,000 pounds Weight of one pole and coil................................ 4,800 pounds Net weight armature punchings.......................... 133,000 pounds Weight top supporting bracket.......................... 58,000 pounds Total weight copper____________...................................... 33,000 pounds Flywheel effect rotor (FR2).............................11,500,000 Shaft and bearings Outside diameter thrust bearing.................................... 49 in. Total bearing surface—-thrust bearing............................. 1,350 in. ..................................... Dimensions upper guide bearing............... 25 in. diameter 42 in. length Maximum diameter shaft........................................... 28 in. Outside diameter shaft flange.................................... 45 in. _____________________________________________________________________________