The distribution of current over the entire cross-section of the conductor is uniform in case of a DC system. But there is an unequal distribution of current over the entire cross-section of the conductor in case of AC system. Here what Skin Effect arises.
What is Skin Effect (SE)?
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When an AC Current flows through a conductor, it is distributed non-uniformly throughout the conductor cross-section. This phenomenon of AC current where it has a tendency to concentrate near the surface of the conductor is called as the skin effect.
Due to the SE, AC current flows between the outer surface of the conductor and the level called skin depth denoted by ẟ as shown in figure 1.
This effect is dependent upon the frequency of the current. The effect becomes more and more apparent as the frequency increases. If the frequency of AC current is very high, the current flow to a very thin skin depth layer. Skin effect increases with increase in the frequency.
The main problem with this effect is that it increases the effective resistance of the conductor for AC. Since the effective cross-section of the conductor through which the current flows is reduced.
So effective resistance of the conductor at moderate to high frequencies is high as compared to the resistance of the same conductor at direct current (DC) and low AC frequencies.
Factors Affecting Skin Effect(SE)
The shape of a conductor, type of material, the diameter of the conductors and operational frequency are the factors that affect the SE.
1. Better conductors and ferromagnetic materials experience higher SE.
2. SE is lesser for stranded conductors than solid conductors
3. SE increases with increase in the cross-sectional area of the conductor.
4. SE increases with increase in the frequency.
How to reduce skin effect?
It can be reduced by using Litz wire or braided wire Litz wire. Another way to reduce this effect by using a stranded conductor.