Skin Effect of Conductors In Transmission Lines
When a conductor is carrying steady direct current (d.c.), this current is uniformly distributed over the whole X-section of the conductor. However, an alternating current flowing through the conductor does not distribute uniformly, rather it has the tendency to concentrate near the surface of the conductor as shown in Fig. This is known as skin effect in transmission lines.
The tendency of alternating current to concentrate near the surface of a conductor is known as skin effect.
Due to skin effect, the effective area of cross-section of the conductor through current flows is reduced. Consequently, the resistance of the conductor is slightly increased when carrying an alternating current. The cause of skin effect can be easily explained. A solid conductor may be thought to be consisting of a large number of strands, each carrying a small part of the current. The inductance of each strand will vary according to its position. Thus, the strands near the center are surrounded by a greater magnetic flux and hence have larger inductance than that near the surface. The high reactance of inner strands causes the alternating current to flow near the surface of conductor. This crowding of current near the conductor surface is the skin effect.
Skin effect depends upon the following factors :
(i) Nature of material
(ii) Diameter of wire − increases with the diameter of wire.
(iii) Frequency − increases with the increase in frequency.
(iv) Shape of wire − less for stranded conductor than the solid conductor.
It may be noted that skin effect is negligible when the supply frequency is low (< 50 Hz) and conductor diameter is small (< 1cm).
