Skin Effect


Skin Effect

Skin effect is a tendency for AC current to flow mostly near the outer surface of an electrical conductor, such as metal wire.  The phenomena of Skin effect is due to unequal distribution of current over the entire cross section of the conductor being used for long distance power transmission is referred as the skin effect in transmission lines.

when electrical power is transmitted through a conductor, it is distributed in the conductor. But large amount of current flows from the outer surface of the conductor and very small amount flows from the inner surface of conductor. So the large amount of current flows from the skin of conductor thats why it is called skin effect. between the outer surface and a level called the skin depth.

Cause Of Skin Effect

The skin effect causes the effective resistance of the conductor to increase at Higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor.  High frequency noise in the range of 1kHz – 1.5MHz increases the inductive reactance of the wire. This forces the electrical charge towards the outer surface of the wire. This means that the total available space of the wire is not used to carry the electrical power.

For Direct Current(DC) through a wire, the resistance of the wire can be calculated from it’s length, diameter and resistivity since it may be assumed that the electric current is essentially uniform over the cross-section of the wire.

The skin effect depends upon the following factors:

  • Conductor material: Better conductors and ferromagnetic materials produces higher skin effect.
  • it is increases with increase in the cross-sectional area.
  • it is increases with increase in the frequency.
  • it is lesser for stranded conductors than solid conductors.

Points to remember

  1. The Skin effect is negligible if the frequency is less than the 50Hz and the diameter of the conductor is less than the 1cm.
  2. In the stranded conductors like ACSR (Aluminium Conductor Steel Reinforced) the current flows mostly in the outer layer made of aluminium, while the steel near the center carries no current and gives high tensile strength to the conductor. The concentration of current near the surface enabled the use of ACSR conductor.


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