Michele Provencher wrote: > > D.H. Kelly wrote: > > > > "Engineering Electromagnetics", William H. Hayt, Jr., McGraw-Hill, 1967, > > Chap 11 "The Uniform Plane Wave" > > Section 5 "Propagation in Good Conductors: the Skin Effect" > > page 344 "Electromagnetic energy is not transmitted in the > > interior of a conductor; it travels in the region surrounding > > the conductor, while the conductor merely guides the waves. > > I remember a variation of this stuff in my textbook, but never > understood the real physical meaning of it. Here are the questions. > > * The power line can have any thickness to carry a large amount of > 60 Hz AC power? > > * If only the surface skin is important, how come the AC power wires > and extension cords are not made of very thin metallic film around > inexpensive plastic core? This would save lots of metal and makes > the power lines much lighter. > > * The DC power, on the other hand, is propagated inside the conductor > metal, doesn't it? Then, one cannot say (DC = AC @ 0 Hz)? The skin depth at 60Hz in copper is about 1/3 inch, so for wires of less than about 2/3 inch diameter you can ignore the skin effect. Very high current high power transmission lines are hollow for the purpose of saving copper and weight. In DC power, the current is uniformly conducted within the copper, but the power is reckoned to be carried by the the fields external to the wire. Opinions expressed herein are my own and may not represent those of my employer.