A single-wire transmission line (or single wire method) is a method of supplying electrical power through a single electrical conductor.
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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, 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]
In 1891 and 1892, Tesla gave demonstration lectures with electrical oscillators before the American Institute of Electrical Engineers at Columbia College, N.Y. and the Institution of Electrical Engineers, London, showing that electric motors and single-terminal incandescent lamps can be operated through a single wire without a return conductor. Electrical capacitance serves to complete the circuit by "electrostatic induction." [2] [3]
In 1893 Tesla stated,
A one-wire transmission system was protected in 1897 by U.S. Patent 0,593,138, "Electrical Transformer". This patent shows a one-wire with earth return circuit.
In 1901 Tesla stated,
A Goubau line, or G-line for short, is a type of single wire transmission line intended for use at UHF and microwave wavelengths.[6] 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. Planar Goubau Lines with applications at terahertz frequencies have also been demonstrated recently.[7]
While Goubau-Line, which uses a conductor having an outer dielectric or special surface conditioning provided to reduce the velocity of the wave on the conductor, has long been known, a more general transverse-magnetic (TM) mode does not have this limitation. Marketed as E-Line, it is similar to Goubau-Lines in its use of launchers 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 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 around an uninsulated conductor without special conditioning and without reducing the wave velocity, while still using launchers of practical size. Conductors much larger than those used by Goubau have been shown to be completely adequate. Furthermore, "a nearby conductor other than the line itself may provide a termination point and thereby reduce energy coupled into the TM wave."[8] This has relevance to Tesla's 1891-1893 table-top demonstrations.
Common uninsulated single or multistrand overhead power conductor may be used to support very low attenuation propagation over the entire frequency range from below 50 MHz to above 20 GHz while employing a launch device of only 15–20 cm in diameter. This makes the installed base of overhead powerlines available for very high rate information transport.[9] Propagation velocity for this line operating in air has been measured to be 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.
Numerical solutions of Maxwell's equations for three dimensional models of simple launcher devices coupling to 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.[8]