Fig. 39.—Power-house on Payette River, Idaho.
All types of water-power stations with direct-connected wheels and generators have much smaller floor areas per unit capacity than do steam-power stations with direct-connected horizontal units. Thus, the modern steam-driven station at Portsmouth, N. H., has a plan area in engine- and boiler-rooms of 16,871 square feet, and its total capacity in four direct-connected units is 4,400 kilowatts, so that the area amounts to 3.82 square feet per kilowatt rating of its generators. Of this area about 46 per cent is in the boiler-room.
Floor Dimensions for Direct-connected, Horizontal
Water-wheels and Generators at Electric Stations.
| Station. | Feet Long. | Feet Wide. | Number of Generators. | Total Kilowatt Capacity. | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| [[A]]Niagara, No. 2 | 496 | 72 | 11 | 41,250 | |||||||||
| Sault Ste. Marie | 1,368 | 100 | 80 | 32,000 | |||||||||
| Colgate | 275 | 40 | 7 | 11,250 | |||||||||
| Electra | 208 | 40 | 5 | 10,000 | |||||||||
| Cañon Ferry | 225 | 50 | 10 | 7,500 | |||||||||
| Red Bridge | 141 | 57 | 6 | 4,800 | |||||||||
| Apple River | - | 140 | 30 | - | 4 | 3,000 | |||||||
| 106 | 22 | ||||||||||||
| Santa Ana River | 127 | 36 | 4 | 3,000 | |||||||||
| Great Falls | 67 | .5 | 55 | 4 | 2,000 | ||||||||
| Garvin’s Falls | - | 62 | 30 | - | 2 | 1,300 | |||||||
| 50 | 23 | ||||||||||||
| Birchem Bend | 56 | .6 | 26 | .7 | 2 | 800 | |||||||
| Portsmouth (steam-driven) | - | 14 | .4 | 119 | .66 | - | 5 | 4,400 | |||||
| inside, but minus 360 square feet. | |||||||||||||
| [A] Vertical wheel shafts. Some of these dimensions apply to the inside and some to the outside of stations. Some small projections are not included. | |||||||||||||
CHAPTER IX.
ALTERNATORS FOR ELECTRICAL TRANSMISSION.
Dynamos in the generating station of an electric transmission system should be so numerous that if one of them is disabled the others can carry the maximum load. If only two generators are installed, it is thus desirable that each be large enough to supply the entire output, so that the dynamo capacity exceeds the greatest demand on the station by 100 per cent. To avoid so great excess of dynamo capacity it is common practice to install more than two generators.
Other considerations also tend to increase the number of dynamos in the generating station of a transmission system. Thus one transmission line may be devoted exclusively to lighting, another to stationary motors, and a third to electric railway service; and it may be desirable that each line be supplied by an independent dynamo to avoid any effect of fluctuations of railway or motor load on the lighting system.
At the generating station of the transmission system that supplies electric light and power in Portland, Me., the idea of independent units has been carried out with four 500-kilowatt dynamos, each driven by a pair of wheels fed with water through a separate penstock from the dam. Each of these dynamos operates one of the four independent transmission circuits. Where a number of water-power stations feed into a single sub-station the requirement that each generating station have its capacity divided up among quite a number of dynamos may not exist, since one station may be entirely shut down for repairs and the load carried meantime by the other stations. A good illustration of this point may be seen at Manchester, where a single sub-station receives energy transmitted from four water-power plants. At one of these plants the entire capacity of 1,200 kilowatts is in a single generator.