CHAPTER X
ELECTRIC POWER STATIONS
It is apparently a very simple matter to fit up a power station with a number of very large dynamos driven by powerful engines, and to distribute the current produced by these dynamos to all parts of a town or district by means of cables, but as a matter of fact it is a fairly complicated engineering problem. First of all the source of power for driving the dynamos has to be considered. In private and other small power plants, gas, petrol or oil engines are generally used, but for large stations the choice lies between steam and water power. In this country steam power is used almost exclusively. Formerly the ordinary reciprocating steam engines were always employed, and though these are still in very extensive use, they are being superseded in many cases by steam turbines. The turbine is capable of running at higher speeds than the reciprocating engine, and at the greatest speeds it runs with a great deal less noise, and with practically no vibration at all. More than this, turbines take up much less room, and require less oil and attendance. The turbines are coupled directly to the dynamos, so that the two machines appear almost as one. In the power station shown on [Plate V]. a number of alternating current dynamos coupled to steam turbines are seen.
A large power station consumes enormous quantities of coal, and for convenience of supply it is situated on the bank of a river or canal, or, if neither of these is available, as close to the railway as possible. The unloading of the coal barges or trucks is done mechanically, the coal passing into a large receiving hopper. From here it is taken to another hopper close to the furnaces by means of coal elevators and conveyors, which consist of a number of buckets fixed at short intervals on an endless travelling chain. From the furnace hopper the coal is fed into the furnaces by mechanical stokers, and the resulting ash and clinker falls into a pit below the furnaces, from which it is carted away.
The heat produced in the furnaces is used to generate steam, and from the boilers the steam passes to the engines along a steam pipe. After doing its work in the engines, the steam generally passes to a condenser, in which it is cooled to water, freed from oil and grease, and returned to the boilers to be transformed once more into steam. As this water from the condenser is quite warm, less heat is required to raise steam from it than would be the case if the boiler supply were kept up with cold water. The power generated by the engines is used to drive the dynamos, and stout copper cables convey the current from these to what are called “bus” bars. There are two of these, one receiving the positive cable from the dynamos, and the other the negative cable, and the bars run from end to end of a large main switchboard. From this switchboard the current is distributed by other cables known as feeders.
The nature of the current generated at a power station is determined to a great extent by the size of the district to be supplied. Generally speaking, where the current is not to be transmitted beyond a radius of about two miles from the station, continuous current is generated; while alternating current is employed for the supply of larger areas. In some cases both kinds of current are generated at one station.
PLATE V.
By permission of
C. A. Parsons & Co.
LOTS ROAD ELECTRIC POWER STATION, CHELSEA.