Generator, Electric, a machine that converts mechanical energy to electrical energy, or, more broadly, any device that converts some form of energy to electrical energy.
The mechanical energy needed to drive a generator is obtained from a prime mover, such as a water turbine, a steam turbine, an internal combustion engine, or a gas turbine. Commonly, dams built across rivers harness a reservoir of water, some of which is led down through pipes to rotate water turbines, which in turn drive generators. These hydroelectric plants are second only to steam-electric plants in producing electricity.
These devices include batteries and fuel cells, which convert chemical energy to electrical energy; photoelectric cells, which convert the energy of light to electricity; and thermoelectric generators, which convert thermal energy to electrical energy.
In a steam-electric plant, coal or oil is burned to change water to steam, and the steam is used to drive a turbine, which in turn drives a large generator. Alternatively, heat generated by a nuclear fission reactor can be used to change water to steam for driving the turbine. The steam turbine is an efficient high-speed prime mover, and it works with the generator to produce most of the world’s electric power.
There are two primary types of rotating machines that convert mechanical energy to electricity: alternating-current (ac) generators and direct-current (dc) generators. Most electricity is now produced by ac generators. These machines, which are also called alternators, synchronous alternators, or synchronous generators, are the main generators in nearly all steam-electric and hydroelectric power plants. The transformer makes it easy to increase alternating voltage for economical transmission and then to decrease it for distribution and use.