The electric supply used for industrial and domestic application is of alternating type. This is so because a highly efficient device called transformer is available. It is capable of transferring electrical energy from one circuit to another at different voltage level. The transformer is used for economically transmitting and distributing electrical power over long distance. This has
permitted us to locate the generation of electric power remotely from the point of demand.
Generally, electric power is generated at about 11kV, then stepped up to higher voltages of 132kV, 220kV and 400kV for transmission lines. At distribution point, it is again stepped down to 400V or 220V for use in industry, offices and homes.
Many applications require the frequency of ac supply to be constant. Constant frequency of generated power can be obtained only if the generator runs at constant speed, called its synchronous speed. Hence, the name synchronous generator. Large size generators are also
called alternators