Single-wire transmission line

A single-wire transmission line (or single wire method) is a method of transmitting electrical power or signals using only a single electrical conductor. This is in contrast to the usual use of a pair of wires providing a complete circuit, or an electrical cable likewise containing (at least) two conductors for that purpose.

The single-wire transmission line is not the same as the single wire earth return system, which is not covered in this article. The latter system relies on a return current through the ground, using the earth as a second conductor between ground terminal electrodes. Thus, the earth effectively forms a second conductor. In a single-wire transmission line there is no second conductor of any form.

As early as the 1780s Luigi Galvani first observed the effect of static electricity in causing the legs of a frog to twitch, and observed the same effect produced just due to certain metallic contacts with the frog involving a complete circuit. The latter effect was correctly understood by Alessandro Volta as an electric current inadvertently produced by what would become known as a voltaic cell (battery). He understood that such a current required a complete circuit to conduct the electricity, even though the actual nature of electric currents was not at all understood (only a century later would the electron be discovered). All subsequent development of electrical motors, lights, etc. relied on the principle of a complete circuit, generally involving a pair of wires, but sometimes using the ground as the second conductor (as with commercial telegraphy).

At the end of the 19th century, Nikola Tesla demonstrated that by using an electrical network tuned to resonance it was possible to transmit electric power using only a single conductor, with no need for a return wire. This was spoken of as the "transmission of electrical energy through one wire without return".

In 1891, 1892, and 1893 demonstration lectures with electrical oscillators before the AIEE at Columbia College, N.Y.C., the IEE, London, the Franklin Institute, Philadelphia, and National Electric Light Association, St. Louis, it was shown that electric motors and single-terminal incandescent lamps can be operated through a single conductor without a return wire. Although apparently lacking a complete circuit, such a topology effectively obtains a return circuit by virtue of the load's self-capacitance and parasitic capacitance.

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