ABSTRACT
In the UK and most developed countries, a large proportion of power supplies is derived through the creation of electricity which is then distributed to consumers via a nationwide transmission grid. The electricity is produced in large-scale units by rotating a generator shaft (the rotor) within a stationary unit (the stator), so that the relative motion of the magnetic field and electric windings on the rotor and stator causes currents to flow in the windings. The mechanical energy of the rotor is provided by a flow of fluid against the blades of the turbine. This flow may be available naturally, as in wind-driven propellors, or as pressurised water in hydroelectric schemes; on the other hand, the energy form available may be unsuitable for such a direct conversion to electricity. In the case of coalfired power, for example, the chemical energy from the reaction of coal with oxygen is converted to heat by burning in air, the heat then being used to boil water. The resulting steam flows against turbine blades to create power as described above. After passage through the turbine, the steam is condensed by flowing through metal tubes cooled by water. The latter can then be discharged to waste if there is an ample water supply, as in the sea, or cooled by air in large cooling towers and reused in the condenser.
