Alternating Current Wiring and Distribution (Classic Reprint) - Softcover

Excerpt from Alternating Current Wiring and Distribution

When a current is started ifl a wire each line or element of increasing current tends to induce counter E. M. R.'s or reverse currents in the metal in its neighborhood; thus all the metal in the Wire is subjected to two opposing forces, one to create current flow and the other to retard it. The cen tral portions Of the wire are surrounded by these retarding influences while the outer surface Of the wire can receive them from one side only. The result Of this is that when a wire is suddenly sub jected to an E. M. F. The current begins first to flow on its surface, and an appreciable time elapses be fore the full current density reaches the centre Of the wire. Thus the current may be said to begin on the outside and soak into the wire. If the al ternations are sufficiently frequent the central por tions of the wire are practically never reached by the current, and the copper available for conduct tivity is little greater than what it would be if the conductor were a tube of similar outside diameter. The thickness of the walls of the equivalent tube will be less as the frequency increases. It is easy to understand that this effect is relatively greater with large wires than with small also, that it will be much greater with iron than with copper wires.

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