Definition: The non-uniform distribution of current through the given cross-section area of the conductor, when it operated on AC current is known as the Skin Effect.
When DC current flows through the conductor it is distributed uniformly throughout the cross-section area of the conductor or skin.
However, an alternating current flowing through the conductor does not distribute uniformly. It concentrates near the surface area of the conductor. this phenomenon is known as the skin effect.
Skin effect is directly proportional to the frequency and diameter of the conductor.
This effect in the transmission line is negligible if the frequency of the supply is less than 50Hz
The main reason for the skin effect is non-uniform flux linkages. Because of this effect, the effective cross-section area of the conductor is reduced. hence the effective resistance of the conductor increases. when the conductor carries AC current.
In the DC system, there is no rate of change of current, and frequency is zero, So current is distributed uniformly throughout the cross-section area of the conductor.
Hence skin effect is absent in the DC system.
In the case of an AC system, Current changes with time, so flux created in the outer strands of the conductor will link with the inner strands due to low reluctances offered by and flux produced by inner strands could link with those strands only not with external strands.
So flux linkage to internal strand increases which will increase internal inductance. Thus the strands near to center are surrounded by a greater magnetic flux.
The Inductance will oppose the flow of current. so current will concentrated on the outer strands of the conductor and a very small current will be allowed through the inner strands.
Factors affecting skin effect in the transmission line
It depends upon the following factors:
- Nature of material: Increase with the increase in the permeability of the material.
- Diameter of conductor: Increases with the diameter of the wire.
- Frequency: The effect increase as the frequency of supply increase.
- Shape of conductor: Less for a stranded conductor than one solid conductor.