Step-up transformers developing very high voltages are not an element of safety in a generator room, and the better practice is to locate them in a separate apartment by themselves, if not in a separate building. For the Niagara Falls plant, the transformers that deliver three-phase current at 22,000 volts are located in a building across the canal from the generating plant. At Cañon Ferry the transformers operating at 50,000 volts, three-phase, are located in a steel and iron addition to the power-house. Transformers at Electra station, which are intended to work ultimately at 60,000 volts, are located in an extension of the main building and are separated from the generator-room by a wall. At the Santa Ana plant the 33,000-volt transformers are grouped in one corner of the generator room, but no partition separates their space from the remainder of the room. In the Colgate plant the transformers, working at 40,000 volts, are spaced along one of the longer sides of the station opposite to and only a few feet from the row of generators. One end of the main room in the Apple River plant is devoted exclusively to the 25,000-volt transformers, and there is a distance of about twenty-seven feet between them and the nearest generator. The highest degree of safety for transformers at these great voltages seems to require that they be located in a separate room where the floor, walls, and roof are made entirely of incombustible material.

Fig. 37.—One of the Turbine Wheels at Spier Falls on the Hudson River.

Water supplied to horizontal turbine wheels under moderate heads usually enters the station by penstocks on one side and leaves it by the tail-race on the other, but this is not true in every case. At the Birchem Bend plant, the canal in which the wheels are located being between the station and the river, water never enters or passes under the station, which has a continuous foundation. So again at the Apple River plant the single supply pipe, twelve feet in diameter and delivering water under a head of eighty-two feet, lies parallel with the greater length of the station and between it and the river. Short penstocks pass from this supply pipe into the wheel section of the power-house, and the water after passing through the wheels flows out to the river between the masonry piers that support the twelve-foot pipe. The generator section of this station has thus no water flowing under it. An interesting distinction may be noted between the conditions as to the tail-water about the foundations of stations working under low and those under great water heads. In cases of the former sort the volumes of water are relatively great and the foundations of stations are usually submerged, and much reduced in area to make room for the tail-races. Thus, the foundations of the station at Red Bridge, where there is 49 feet head, have nearly all of their footings under water, and of a total length of 145 feet at the top of these foundations the six tail-races underneath cut out 92 feet. These tail-races extend underneath both the wheel and generator rooms.

Where power is derived from water delivered under great head from pipe nozzles to impulse-wheels, stations are usually well above the water levels of streams into which they discharge, and passages for tail-water underneath the station shrink to small tunnels through their foundations. Seven of these tunnels have a total width of less than 25 feet at the Santa Ana River station, which is 127 feet long, and where the head of water is 728 feet. At the Colgate plant, with its head of 700 feet, the water, at times of light load, instead of flowing out of its passages underneath the station, shoots from the pipe nozzles clear across the North Yuba River on the bank of which the station stands.

Fig. 38.—Power Plant of Ludlow Manufacturing Company.

[Larger section] (173 kB)

In a comparison of floor areas per kilowatt of main generator capacities in electric stations using water- and those using steam-power, the matter of space for transformers may be entirely omitted, because the extent of this space is independent of the type or location of water-wheels, or the difference of water and steam as motive powers. Where water-wheels and their connected generators occupy separate rooms, as is often the case with turbines under low pressures, the wheel room has a little less length, and is generally narrower than the generator room. Thus, at the Red Bridge station the generator room is 141 feet long and the wheel room about 127 feet, while the former is 33.33 feet and the latter 24 feet wide. So again at Apple River Falls the generator room is 140 by 30 feet and the wheel room 106 by 22 feet, the generator room in this case containing also transformers. It follows that if wheels can be located outside of the station, as in a canal, quite a reduction in its total floor area can be made, which may easily range from 20 to 40 per cent. The kilowatt capacity per square foot of floor area in both wheel and generator rooms combined tends to increase with the individual capacity of the generating units. Generators on vertical shafts seem to require about as much floor space per unit of capacity as do generators on horizontal shafts. In the Red Bridge station the total capacity is 4,800 kilowatts of main generators in six horizontal units, and the area of the generator room alone is 0.96 square foot per kilowatt of this capacity. The second station with vertical units at Niagara Falls has a capacity of 41,250 kilowatts in eleven generators on vertical shafts, and its floor area amounts to 0.86 square foot per kilowatt; narrow impulse-wheels of large diameter tend to economy of floor space, as in Electra station, where the room containing wheels and generators has an area of only 0.83 square foot per unit of its 10,000 kilowatts capacity. At the Colgate plant, where the total rating of generators is 11,250 kilowatts, the floor area under wheels and generators is almost exactly one square foot per kilowatt. The Santa Ana station, with a total capacity of 3,000 kilowatts, has 1.52 square feet of floor area for each unit of capacity. This last figure may be compared with the 1.72 square feet per kilowatt of generator rating for the 4,800-kilowatt station at Red Bridge and the 1.75 square feet per unit of capacity in the 800-kilowatt plant at Birchem Bend.