Electric generators Alternating current

An alternator (or synchronous generator) is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current (AC). For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. The rotor coil is externally excited by a small direct current (DC), while the AC is generated in the stationary coils. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. Although any AC electrical generator might be called an alternator, usually the term refers to small rotating machines driven by automotive and other internal combustion engines. The term usually applies those types with externally excited rotor coils. An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators. Large 50 or 60 Hz three-phase alternators in power plants generate most of the world's electric power, which is distributed by electric power grids.