What is Skin effect?The distribution of current over the cross section of the conductor is uniform in DC only. In alternating current flow through a conductor does not distribute uniformly but it will concentrate near the surface of the conductor. In fact, in AC system no current flow through the core because the whole current will flow through the surface region. Due to this reason the effective area of conductor is reduced causing an increase in AC resistance .The effective AC resistance is usually referred as the effective resistance of the conductor .This phenomenon is called the Skin effect as it will cause concentration of current at the skin of conductor.
Skin effect can easily explain by considering a solid conducting to be composed of a large number of angular filaments ,each carrying a fraction of total current. The flux linkage due to the filaments lying at the surface link the whole of the conductor while the flux setup due to the inner filaments does not link with the surface or outer filaments. Thus the filaments near the surface are of large inductance then that near the outer surface .The high reactance of the inner filament causes the current to distribute in such a way that the current density is less in the interior of the conductor then at the surface of conductor. The distribution of current over the section of conductor is therefore, be non uniform
Skin effect depend upon the following things
- It depend upon type of material
- Depend upon frequency
- Diameter of conductor
- shape of conductor
At low frequency the effect is very small ,in fact it is only of important with high frequency or with solid conductors of large cross-section. For commercial frequency 0f 50 Hz or less the increase in effective resistance is inappropriate for solid copper conductor up to 1 cm in diameter: and 2.5 percent for 2 cm diameter and 8 percent for 2.5 cm diameter.In aluminum conductor the effect are same as that of copper wire of equal conductivity.
With stranded conductor skin effect is much smallest than with solid conductors. It will increase with increase of cross-section, permeability and supply frequency.
In practice stranded conductors are mostly used for transmission and distribution lines and hollow conductors are used for solid bus -bar ..This will reduce the effect of skin effect .
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