Electric generator
Converts mechanical energy to electrical energy for external circuits.
An electric generator, also called an electrical generator or electromagnetic generator, is an electromechanical device that converts mechanical energy into electrical energy for use in an external circuit. In most rotating generators, a source of kinetic power rotates the shaft, producing an electric current at the output terminals that flows through an external circuit to power electrical loads. Mechanical energy sources include steam turbines, gas turbines, water turbines, internal combustion engines, wind turbines, and hand cranks. Generators supply nearly all electricity for global power grids. The first electromagnetic generator, the Faraday disk, was invented by Michael Faraday in 1831. The reverse conversion—electrical to mechanical energy—is performed by an electric motor; motors and generators are very similar, and some motors can operate as generators if their shaft is rotated.
Electromagnetic generators fall into two categories: dynamos, which produce pulsing direct current via a commutator, and alternators, which generate alternating current. Mechanically, a generator has a rotating part (rotor) and a stationary part (stator) forming a magnetic circuit. One part generates a magnetic field using field windings or permanent magnets; the other contains armature windings where the changing field induces current. The armature can be on either the rotor or stator. Electrically excited generators include an excitation system for field flux; permanent magnet generators are called magnetos or permanent magnet synchronous generators.
Before electromagnetism was understood, electrostatic generators used moving charged belts or disks to produce very high voltage and low current via electrostatic induction or the triboelectric effect. Inefficient and difficult to insulate, they had low power ratings and were never used for commercial power, only for early X-ray tubes and some particle accelerators. Faraday’s disk, a homopolar generator, produced a small DC voltage but suffered from self-cancelling counterflows outside the magnetic field, limiting output and causing waste heat. Later homopolar designs used an array of magnets around the disk perimeter to maintain steady current flow. Experimenters found that multiple wire turns in a coil produced higher, more useful voltages, making wire windings a standard feature of all subsequent generators.
- first electromagnetic generator
- Faraday disk, invented 1831 by Michael Faraday
- categories
- dynamos (DC) and alternators (AC)
- key components
- rotor, stator, field winding or permanent magnets, armature
- first industrial generator
- Woolrich Electrical Generator of 1844
- self-excitation discovered by
- Ányos Jedlik (independently of Faraday)
Lore & Background
The operating principle of electromagnetic generators was discovered in 1831–1832 by Michael Faraday, later called Faraday's law of induction. Faraday built the first electromagnetic generator, the Faraday disk, a homopolar generator using a copper disc rotating between the poles of a horseshoe magnet, which produced a small DC voltage. This design was inefficient due to self-cancelling counterflows and low output voltage; later designs used multiple turns of wire in coils to produce higher voltages.
Independently of Faraday, Ányos Jedlik began experimenting in 1827 with electromagnetic rotating devices and discovered the principle of dynamo self-excitation, which replaced permanent magnet designs. The first practical electric generators, called dynamos, used a commutator to convert alternating current into pulsing direct current. The Woolrich Electrical Generator of 1844 was the earliest generator used in an industrial process, for commercial electroplating.
The modern dynamo was invented independently by Sir Charles Wheatstone, Werner von Siemens, and Samuel Alfred Varley in 1866–1867. Their designs employed self-powering electromagnetic field coils rather than permanent magnets, greatly increasing power output and enabling the first major industrial uses of electricity. The dynamo was later succeeded by the AC alternator, or synchronous generator, which generates alternating current and is directly connected to the grid.
Reader's Guide
Electric generators are fundamental to modern civilization, as they produce nearly all electric power for worldwide grids. The invention of the electromagnetic generator by Michael Faraday in 1831 established the principle of electromagnetic induction, which remains the basis for all subsequent generator designs. The transition from inefficient early designs like the Faraday disk to wire-wound coils allowed generators to produce useful voltages for industrial applications. The development of the dynamo with self-exciting electromagnetic field coils by Siemens, Wheatstone, and Varley in the 1860s marked a turning point, enabling high-power generation and leading to the first major industrial uses of electricity, such as powering electric arc furnaces. The later adoption of alternating current and synchronous generators allowed efficient long-distance power distribution through voltage transformation. While large DC dynamos are now rare, the basic principles of the generator—a rotating part (rotor) and a stationary part (stator) forming a magnetic circuit—continue to underpin all modern power generation, from steam and gas turbines to wind and water turbines. The term generator also extends to photovoltaic, fuel cell, and magnetohydrodynamic devices that use solar power or chemical fuels.
Did You Know?
- The first electromagnetic generator, the Faraday disk, was invented in 1831 by Michael Faraday.
- The Woolrich Electrical Generator of 1844 is the earliest electrical generator used in an industrial process, for commercial electroplating.
- The modern dynamo was independently invented by Sir Charles Wheatstone, Werner von Siemens, and Samuel Alfred Varley in 1866–1867.
- Some electric motors can be used in reverse as generators if their shaft is rotated.
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