In any power house adequate provision for reserve capacity evidently can be most easily made if the equipment throughout is of a single kind so that everything may be as far as pos sible interchangeable. Similar units of uniform size are, therefore, advisable throughout the entire plant unless there is some good reason to the contrary.
The equipment of a power house may be divided into four parts: the prime movers, the electric generators, the accessory apparatus, and the switchboard, from which the output is regu lated and distributed. The power-house struc ture must be planned for advantageous loca tion of all of these and in addition, if steam is the motive power, there must be ample provision for the storage of fuel.
Design and point of de sign hydro-electric power houses present by far the simplest problem. In these the prime movers are the water wheels, which are rela tively simple and compact, the generators are directly coupled to the shafts of these, and the output is delivered to a small number of lines so that the switchboard is relatively simple. As most such plants are for high voltage, the power house must often provide place for the transformers which raise the voltage from that of the generators to that of the line. Less frequently such transformers are found in steam-driven plants.
Structurally the ordinary power house con sists of two parallel halls with a common di viding wall, one containing the generating units, the other water wheels or boilers as the case may be. The generator room contains or has aimexed to it space for the switchboard con nections and for the transformers, if any, while the boiler or wheel room has annexed to it space on the one hand for fuel, on the other for the hydraulic connections. Usually the plant comprises only a single story, although more rarely ground space is gained by superimpos ing some of the parts.
One may now pass to consideration of the concrete arrangements usually adopted, the hydro-electric case being taken up first: as the simpler in design.
Fig. 1 shows the small plan of a typical hydro-electric power station using as prime movers water wheels under high head. Here A
is the receiver terminating the supply pipe and provided with branches to the several wheels. At very high heads these branches are some times made farther back, spreading finger-wise from a terminal chamber to secure a straighter run to the wheels. B, B, B are the water wheels, directly coupled to and on the same level with the generators C, C, C. The pipes from the water supply enter the lower part of this case the inner tail-race wall would usually carry a partition wall separating the wheel room from the dynamo room proper and pro vided with water-tight fittings for the turbine shafts to pass through.
In case raising transformers were to be used in such a plant the generators would be for perhaps 2,300 volts, the switchboard would preferably be turned around, facing the ex citers, and the station would be extended far enough to the left of the cut to accommodate the transformers and the necessary accessories; or, if more convenient from the nature of the ground, space could be gained by widening the power house enough to accommodate the row of transformers. The size of the power house of Fig. 1 is about 40 feet by 85 feet and slight modifications of this simple design serve the wheel cases and discharge into the tail race below the power-house floor. The wheel gates are controlled by the governors D, D, D. The generators are revolving-field, 400 kilowatts, three-phase machines, giving 13,000 volts at the terminals at 500 revolutions per minute. Their fields are excited by two 25-kilowatt direct driven exciters, E, E, each of which is regu lated by a separate hydraulic governor. The switchboard is located on the floor level at F, and the line wires leaves the power house just above and behind the switchboard. Room is provided for a fourth generator and a traveling crane running lengthwise the power house is available for handling the machinery if neces sary. The material of this power house is brick, on concrete foundations, with a steel truss roof covered with reinforced concrete slabs and then with roofing felt and asphalt, as the location is in a cold climate.