References: 1. Langdon Crane, Magnetohydrodynamic (MHD) Power Generator: More Energy from Less Fuel, Issue Brief Number IB74057, Library of Congress Congressional Research Service, 1981, retrieved from http://digital.library.unt.edu/govdocs/crs/permalink/meta-crs-8402:1 July 18,2008 2. Horst Bauer Bosch Automotive Handbook 4th Edition Robert Bosch GmbH, Stuttgart 1996 ISBN 0-8376-0333-1, page 813 3. Rudolf F. Graf, "Dictionary of Electronics; Radio Shack, 1974-75". Fort Worth, Texas. 4. Nikola Tesla, "Notes on a Unipolar Dynamo". The Electrical Engineer, N.Y., Sept. 2, 1891. (Also available at tesla.hu, Article 18910902) 5. Rudolf F. Graf, "Dictionary of Electronics; Radio Shack, 1974-75". Fort Worth, Texas. 6. Thomas Valone, "Harnessing the Wheelwork of Nature : Tesla's Science of Energy", The Homopolar Generator: Tesla's Contribution. ISBN 1-931882-04-5 (ed. originally presented in the Proceedings of International Tesla Symposium, 1986, p. 6-29) 7. Hannes Alfvén and Carl-Gunne Fälthammar, Cosmical Electrodynamics (1963) 2nd Edition, Oxford University Press. See sec. 1.3.1. Induced electric field in uniformly moving matter. 8. Hill, T. W.; Dessler, A. J.; Rassbach, M. E., "Aurora on Uranus - A Faraday disc dynamo mechanism" (1983) Planetary and Space Science (ISSN 0032-0633), vol. 31, Oct. 1983, p. 1187-1198 9. Hannes Alfvén, "Sur l'origine de la radiation cosmique" (On the origin of cosmic radiation)" Comptes Rendus, 204, pp.1180-1181 (1937) Hakala, Pasi et al, "Spin up in RX J0806+15: the shortest period binary" (2003) Monthly Notice of the Royal Astronomical Society, Volume 343, Issue 1, pp. L10-L14 11. Burns, M. L.; Lovelace, R. V. E., "Theory of electron-positron showers in double radio sources" (1982) Astrophysical Journal, Part 1, vol. 262, Nov. 1, 1982, p. 87-99 Shatskii, A. A., "Unipolar Induction of a Magnetized Accretion Disk around a Black Hole", (2003) Astronomy Letters, vol. 29, p. 153-157 13. Per Carlqvist, "Cosmic electric currents and the generalized Bennett relation" (1988) Astrophysics and Space Science (ISSN 0004-640X), vol. 144, no. 1-2, May 1988, p. 73-84.
14. Goldreich, P.; Lynden-Bell, D., "Io, a jovian unipolar inductor" (1969) Astrophys. J., vol. 156, p. 59-78 (1969). 15. Strobel, Darrell F.; et al, "Hubble Space Telescope Space Telescope Imaging Spectrograph Search for an Atmosphere on Callisto: A Jovian Unipolar Inductor" (2002) The Astrophysical Journal, Volume 581, Issue 1, pp. L51-L54 16. "Sonett, C. P.; Colburn, D. S., "Establishment of a Lunar Unipolar Generator and Associated Shock and Wake by the Solar Wind" (1967) Nature, vol. 216, 340-343. 17. Schwartz, K.; Sonett, C. P.; Colburn, D. S., "Unipolar Induction in the Moon and a Lunar Limb Shock Mechanism" in The Moon, Vol. 1, p.7 18. Srnka, L. J., "Sheath-limited unipolar induction in the solar wind" (1975) Astrophysics and Space Science', vol. 36, Aug. 1975, p. 177-204. 19. Yang, Hai-Shou, "A force - free field theory of solar flares I. Unipolar sunspots" Chinese Astronomy and Astrophysics, Volume 5, Issue 1, p. 77-83. 20. Osherovich, V. A.; Garcia, H. A., "Electric current in a unipolar sunspot with an untwisted field" (1990) Geophysical Research Letters (ISSN 0094-8276), vol. 17, Nov. 1990, p. 2273-2276. 21. Eroshenko, E. G., "Unipolar induction effects in the Venusian magnetic tail" (1979) Kosmicheskie Issledovaniia, vol. 17, Jan.-Feb. 1979, p. 93-10 22. John David Jackson, Classical Electrodynamics, Wiley, 3rd ed. 1998, ISBN 0-471-30932-X 23. Olivier Darrigol, Electrodynamics from Ampere to Einstein, Oxford University Press, 2000, ISBN 0-19-850594-9 24. Trevor Ophel and John Jenkin, (1996) Fire in the belly : the first 50 years of the pioneer school at the ANU Canberra : Research School of Physical Sciences and Engineering, Australian National University. ISBN 0-85800-048-2. (PDF) 25. Thomas Valone, The Homopolar Handbook : A Definitive Guide to Faraday Disk and N-Machine Technologies. Washington, DC, U.S.A.: Integrity Research Institute, 2001
An electrical generator is a device that converts kinetic energy to electrical one, generally using electromagnetic induction.
The reverse conversion of electrical energy into mechanical energy is done by a motor. Motors and generators have many similarities in its constructions .
The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, or any other source of mechanical energy.
The Dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses electromagnetic principles to convert mechanical rotation into a pulsing direct electric current through the use of a commutator. A dynamo machine consists of a stationary structure, which provides a constant magnetic field, and a set of rotating windings which turn within that field.
On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils.
The first dynamo based on Faraday's principles was built in 1832 by Hippolyte Pixii, a French instrument maker. It used a permanent magnet which was rotated by a crank. The spinning magnet was positioned so that its north and south poles passed by a piece of iron wrapped with wire.
Pixii found that the spinning magnet produced a pulse of current in the wire each time a pole passed the coil. Furthermore, the north and south poles of the magnet induced currents in opposite directions. By adding a commutator, Pixii was able to convert the alternating current to direct current.
Unlike the Faraday disc, many turns of wire connected in series can be used in the moving windings of a dynamo. This allows the terminal voltage of the machine to be higher than a disc can produce, so that electrical energy can be delivered at a convenient voltage.
The relationship between mechanical rotation and electric current in a dynamo is reversible; the principles of the electric motor were discovered when it was found that one dynamo could cause a second interconnected dynamo to rotate if current was fed through it.
Other Rotating Electromagnetic Generators
Without a commutator, the dynamo is an example of an alternator, which is a synchronous singly-fed generator. With an electromechanical commutator, the dynamo is a classical direct current (DC) generator. The alternator must always operate at a constant speed that is precisely synchronized to the electrical frequency of the power grid for non-destructive operation. The DC generator can operate at any speed within mechanical limits but always outputs a direct current waveform.
The alternator must always operate at a constant speed that is precisely synchronized to the electrical frequency of the power grid for non-destructive operation. The DC generator can operate at any speed within mechanical limits but always outputs a direct current waveform.
Other types of generators, such as the asynchronous or induction singly-fed generator, the doubly-fed generator, or the brushless wound-rotor doubly-fed generator, do not incorporate permanent magnets or field windings that establish a constant magnetic field, and as a result, are seeing success in variable speed constant frequency applications, such as wind turbines or other renewable energy techologies.
The full output performance of any generator can be optimized with electronic control but only the doubly-fed generators or the brushless wound-rotor doubly-fed generator incorporate electronic control with power ratings that are substantially less than the power output of the generator under control, which by itself offer cost, reliability and efficiency benefits
A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery.
MHD generators were originally developed because the output of a plasma MHD generator is a flame, were able to heat the boilers of a steam power plant.
The first practical design was the AVCO Mk. 25, developed in 1965. The U.S. government performed substantial development, culminating in a 25Mw demonstration plant in 1987. MHD generators operated as a topping cycle are currently (2007) less efficient than combined-cycle gas turbines.
The generator moves an electric current, but does not create electric charge, which is already present in the conductive wire of its windings. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside.
Other types of electrical generators exist, based on other electrical phenomena such as piezoelectricity and magnetohydrodynamics. The construction of a dynamo is similar to that of an electric motor, and all common types of dynamos could work as motors.
The parts of a dynamo can be expressed in either mechanical terms or electrical terms. Although distinctly separate, these two sets of terminology are frequently used interchangeably or in combinations that include one mechanical term and one electrical term. This causes great confusion when working with compound machines such as a brushless alternator or when conversing with people who work on a machine that is configured differently than the machines that the speaker is used to.
Mechanical Rotor: The rotating part of an alternator, generator, dynamo or motor. Stator: The stationary part of an alternator, generator, dynamo or motor.
Electrical Armature: The power-producing component of an alternator, generator, dynamo or motor. The armature can be on either the rotor or the stator. Field: The magnetic field component of an alternator, generator, dynamo or motor. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator.