Single-wire transmission line
From Wikipedia, the free encyclopedia
A single-wire transmission line (or single wire method) is a method of supplying electrical power through a single-wired electrical conductor. Single wire earth return (SWER) or single wire ground returns today supply single-phase electrical power to remote areas at low cost.
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[edit] History
In 1729, the English physicist Stephen Gray noticed the phenomenon of electrical conductivity. Essentially, electric currents may be transmitted from one body to another along a conductor, and all conductors contain movable charges of electricity. At the end of the 19th century, Nikola Tesla demonstrated that by using an electrical network tuned to resonance and using, what at the time would be called, "high frequency AC" and today would be low frequency AC, only a single wire was necessary for power systems, with no need for a metal or Earth return conductor. Tesla called it the "transmission of electrical energy through one wire without return". [1] Tesla stated in 1901,
- "Some ten years ago, I recognized the fact that to convey electric currents to a distance it was not at all necessary to employ a return wire, but that any amount of energy might be transmitted by using a single wire. I illustrated this principle by numerous experiments, which, at that time, excited considerable attention among scientific men." [2]
In the spring of 1891, Tesla gave demonstrations with various machines before the American Institute of Electrical Engineers at Columbia College. His lecture exhibited this feature, the chief import exhibited that all kinds of devices could be operated through a single wire without a return conductor. The one-wire transmission system was protected in 1897 by U.S. Patent 0,593,138, "Electrical Transformer".
[edit] Goubau lines
A Goubau line, or G-line for short, is a type of single wire transmission line intended for use at UHF and microwave wavelengths. [3] The line itself consists of a single conductor coated with dielectric material. Coupling to and from the G-line is done with conical metal "launchers" or "catchers," with their narrow ends connected for example to the shield of coaxial feed line, and with the transmission line passing through a hole in the conical tips.
[edit] E-Line
While Goubau-Line, which uses a conductor having an outer dielectric or special surface conditiong provided to reduce the velocity of the wave on the conductor, has long been known, a more general mode has recently been discovered and demonstrated which does not have this limitation. "E-Line" is similar to Goubau-Lines in its use of launching horns to couple to and from a radially symmetric wave propagating in the space around a single conductor but different in that it can operate on insulation-free conductors, including those that are polished and completely unfeatured. The propagation velocity of the wave is not reduced by dielectric and is accordingly quite close to that of a wave traveling in the same medium in the absence of any conductor at all.
Contrary to Goubau's assertions, it has been shown both possible and practical to launch a surface wave on an uninsulated conductor without special conditioning and without reducing the wave velocity, while still using launches of practical size. In addition, conductors much larger than those used by Goubau have been shown to be completely adequate.
Of particular practical value, common uninsulated single or multistrand overhead power conductor may be used to support very low attenuation propagation over the entire frequency range from below 200 MHz to above 10 GHz while employing a launch device of only 15-20 cm in diameter. This makes available the worldwide installed base of overhead powerline for very high rate information transport. Measured propagation velocity for this line operating in air is within 0.1% of that of a free wave in air. The effects of line taps, bends, insulators and other impairments normally found on power distribution systems have proven to be predictable and manageable.
Although an analytical treatment of this wave guide which corrects the previous work of Goubau has not yet been presented, numerical solutions of Maxwell's equations for three dimensional models of simple launch devices with an ideal, smooth conductor have confirmed the low attenuation, high bandwidth, high propagation velocity and that the vast majority of the propagated energy remains quite close to the conductor surface, all in agreement with measurement.
[edit] See also
[edit] Patents
- U.S. Patent 6,104,107, "Method and apparatus for single line electrical transmission". Avramenko, et al.
- U.S. Patent 2,685,068, "Surface wave transmission line". George J. E. Goubau
- U.S. Patent 2,921,277, "Launching and receiving of surface waves". George J. E. Goubau.
- U.S. Patent 7,009,471, "Method and apparatus for launching a surfacewave onto a single conductor transmission line using a slotted flared cone". Glenn E Elmore
- US patent application 20050258920 " System and method for launching surface waves over unconditioned lines " Glenn E Elmore
[edit] References and notes
- Citations
- ^ "Why did Tesla make his coil in the first place? What was it that he was trying to accomplish? Other than just the fun of making one, do they have any practical purposes?", tfcbooks.com.
- ^ Nikola Tesla, "Talking with the Planets (1901)". Collier's Weekly, February 19, 1901, page 4-5
- ^ Geog Goubau, "Surface waves and their Application to Transmission Lines," Journal of Applied Physics, Volume 21, Nov. (1950)
[edit] Further reading
- Toby Grotz, "Wireless Transmission of Power, An Attempt To Verify Nikola Tesla's 1899 Colorado Springs Expriments, Results Of Research And Experimentation". Proceedings of the 26th IECEC Conference, vol. 4 (1991).
- N. Tesla, "The True Wireless". Electrical Experimenter (May 1919).
- J.J. O'Neill, "Prodigal Genius, The life of Nikola Tesla" (Neville Spearman 1968) pp. 70-73, 128-133.
- John O'Neill, "Electrical Prometheus" (History of Technology ("Molodaya Gvardiya") 1959).
