POWER HOUSES. With the growth of electrical distribution, the generating station has become a highly specialized structure which de mands consideration both from the electrical and mechanical viewpoints. In the first instance it presents peculiar requirements as to location, differing widely according to its purpose. Broadly, one may divide power houses into two general classes, those designed for the utilization of water power and those using heat engines as prime movers. The former are nearly always power transmission stations con nected by high tension lints with the centre of distribution and not themselves burdened with direct distribution of energy to consumers. The latter are generally within the area of distribu tion, and the centres of distributing net works. In the cases where power is transmitted con siderable distances from stations of the second class they are still generally to be regarded as distributing stations as regards the requirements of location.
Location.— The location of hydro-electric power houses is usually determined by purely hydraulic considerations. The area within which they may be economically placed is lim ited by the topography, and the chief require ments are as follows: First, the location must be such as to keep the power house free of floods under all conditions of stream flow. Sec ond, within this limitation the location must be such as to utilize the maximum possible pro portion of the available head. Third, in the interest of regulation the station must be placed so that it may be subject to the minimum variation of head. In plants working under high hydraulic heads, high enough to utilize impulse wheels conveniently, these conditions are easily met. At low heads there is often difficulty in placing the power house clear of floods and above any possible backing up of the tail water.
The location of a station driven by heat engines of one sort or another is usually kept as nearly as may be at the centre of the elec trical distribution. Since for the delivery of any given load at a fixed percentage of loss the weight of conductor required varies directly with the square of the distance from the load, the reason for a central location is obvious. Assuming, for example, an electrical load uni formly distributed over a circular area, the most economical location of the power station, so far as the conductors are concerned, is at the centre. Transference of the station to a point
at the edge of the area approximately doubles the cost of the distributing system. The causes which may justify removal from the central position are local conditions as to cost of real estate, of fuel and of water. The first item is part of the capital charge which may be taken as an offset to change in the cost of dis tribution; the last two affect the operating ex pense, and the change in these with change of location must be capitalized for comparison with the concurrent change in the cost of dis tribution.
Fuel.— Fuel is by far the largest single item of expense in ordinary electrical power production, and a power house must be so lo cated, on a railway spur or waterway, that it can receive its supply and secure proper storage space without incurring serious charges for cartage or other handling of fuel. This neces sity usually compels a location somewhat out of the centre of distribution. Water supply is more easily secured, but occasionally it becomes an important factor in location. In cases where the principal office of the power station itself is to furnish energy at high voltage for a dis tribution from substations, the cost of con ductors is relatively a smaller consideration and commonly a location meeting the requirements just laid down can be secured without serious increase in the cost of the conducting system.
The electrical equipment of a modern power station usually consists of a small number of electric generators directly coupled to their prime movers, whether hy draulic, steam or gas operated. Except in small plants generators driven through inter mediary belts, ropes or gears are rare, since these introduce added complications, cause some loss of energy, cannot well be used for large power, and serve no useful purpose of them selves, save now and then in giving the gen erators some specially valuable advantage in speed. In such case they should be used with out hesitation if the conditions permit. The day of stations equipped with numerous small dynamos has passed, and for good cause, since the small machines are more costly and less efficient for a given total output, and they re quire also more space and more care.