ELECTRIC GENERATOR

also called dynamo, any machine that converts mechanical energy to electricity for transmission and distribution over power lines to domestic, commercial, and industrial customers. Generators also produce the electrical power required for automobiles, aircraft, ships, and trains. The mechanical power for an electric generator is usually obtained from a rotating shaft and is equal to the shaft torque multiplied by the rotational, or angular, velocity. The mechanical power may come from a number of sources: hydraulic turbines at dams or waterfalls; wind turbines; steam turbines using steam produced with heat from the combustion of fossil fuels or from the fission of heavy atomic nuclei; gas turbines burning gas directly in the turbine; or gasoline and diesel engines. The construction and the speed of the generator may vary considerably depending on the characteristics of the mechanical prime mover. Nearly all generators used to supply electric power networks generate alternating current, which reverses polarity at a fixed frequency (usually 50 or 60 cycles, or double reversals, per second). Since a number of generators are connected into a power network, they must operate at the same frequency for simultaneous generation. They are therefore known as synchronous generators or, in some contexts, alternators. also called Dynamo, any machine that converts mechanical energy to electricity for transmission and distribution over electrical power networks or for use in trains, ships, aircraft, and automobiles. Electric generators transform mechanical energy from various sources, as, for example, wind turbines, water turbines at dams, steam turbines driven by steam produced with heat from the combustion of fossil fuels or from nuclear fission, and internal-combustion engines (diesel engines and gas-turbine engines in particular). The construction and speed of generators vary according to the characteristics of the mechanical prime mover employed. The underlying principles of operation of an electric generator are the same as those for an electric motornamely, Ampre's law and Faraday's law of induction (see also electric motor). In an electric motor, the flow of energy is simply reversed, with electrical energy undergoing conversion to mechanical energy. In most cases, generators that supply electrical power networks produce alternating current (AC), which reverses polarity at a fixed frequency (generally 50 or 60 cycles per second). Several generators are usually connected into a power network and must operate at the same frequency for simultaneous power generation. Such machines are called synchronous generators or, sometimes, alternators. The first practical electric generator was built by the French engineer and inventor Znobe-Thophile Gramme during the late 1860s. This so-called Gramme dynamo contributed significantly to the general acceptance of electricity as a useful form of energy. Additional reading Overviews may be found in the following texts: Syed A. Nasar (ed.), Handbook of Electric Machines (1987); G.R. Slemon and A. Straughen, Electric Machines (1980); Syed A. Nasar and L.E. Unnewehr, Electromechanics and Electric Machines, 2nd ed. (1983); Vincent Del Toro, Electric Machines and Power Systems (1985); and George McPherson and Robert D. Laramore, An Introduction to Electrical Machines and Transformers, 2nd ed. (1990). Gordon R. Slemon