[Illustration: FIG. 35.--Plan and Elevation of Red Bridge Station on the Chicopee River.]
Modern electric stations driven by water-power are usually but one story in height and are clear inside from floor to roof, save for cranes and roof trusses. This construction may be seen in the Niagara, Spier Falls, Cañon Ferry, Colgate, Electra, Santa Ana River and many other notable plants. In spite of this one-story style of construction, the electric stations reach fair elevations because of the necessity for head room to operate cranes in placing and removing generators. At Garvin’s Falls, on the Merrimac River, the electric station contains generators of 650 kilowatts each and the distance from floor to the lower cords of roof trusses is 27 feet. In the station at Red Bridge, on the Chicopee River, where generators are of 1,000 kilowatts capacity each, the distance between floor and the under side of roof beams is 30.66 feet. Between the floor and roof trusses at the Birchem Bend station, on the river last named, the distance is 26.25 feet, but each generator is rated at only 400 kilowatts. In the Cañon Ferry plant, with its generators of 750 kilowatts each, the distance from floor to roof trusses is 28 feet. At the plant on Santa Ana River, the 750-kilowatt generators, being connected to impulse-wheels, operate at 300 revolutions per minute, have relatively small diameters and are mounted over pits in the floor so that their shaft centres are only about two feet above it. By these means the distance from floor to roof trusses was reduced to 18.25 feet. All these examples of elevations between floors and roof supports are for stations with direct-connected generators and horizontal wheels. In the new Niagara station, where generators of 3,750 kilowatts each are mounted on vertical wheel shafts that rise from the floor, the distance between the floor and roof trusses is 39.5 feet.
Electric stations driven by water-power are now constructed almost entirely of materials that will not burn--that is, stone, brick, tile, concrete, cement, iron, and steel. Stone masonry laid with cement mortar or concrete masonry is very generally employed for all those parts of the foundations that come in contact with the tail-water. For sub-foundations bedrock is very desirable, but where this cannot be reached piles are driven closely and their tops covered with several feet of cement concrete as a bedding for the stone foundation. Where stone is plenty or bricks hard to obtain, the entire walls of a water-power station are frequently laid entirely with stone in concrete mortar. If bricks can readily be had they are more commonly used than stone for station walls above the foundations. Concrete formed into a monolithic mass is a favorite type of construction for the foundations, walls and floors of water-power plants in Southern California. Cement and concrete are much used for station floors in all parts of the country, and these floors are supported by masonry arches in cases where the tail-water flows underneath the station after leaving the wheels. Station roofs are usually supported by steel trusses or I-beams, and slate and iron are favorite roof materials. With iron roof-plates an interior lining of wood, asbestos, or some other poor conductor of heat is much used to prevent the condensation of water on the under side of the roof in cold weather. Walls of water-power stations are usually given sufficient thickness of masonry to support all loads that come upon them without the aid of steel columns. In some cases where cranes do not extend entirely across their stations, one end of each crane is supported by one of the station walls and the other end by a row of iron or steel columns rising from the floor. Where the generator-room of a station has its floor level below high-water mark especial care should be taken to make the walls water-proof to an elevation above this mark. As the travelling-crane and the loads which it carries in erecting wheels and generators form a large part of the weight on the station walls, these walls are often reduced as much as one-half in thickness at the level of the crane, thus forming benches on which the ends of the cranes rest.