A. the resistivity of the transmission line
B. the current magnitude in the transmission line
C. the cross-sectional area of the transmission line
D. the voltage applied across the transmission line
Answer: C. the cross-sectional area of the transmission line
Explanation:
The phenomenon arising due to unequal distribution of current over the entire cross-section of the conductor is referred to as the skin effect.
Such a phenomenon does not have much role to play in case of a very short transmission line, but with an increase in the effective length of the conductors, skin effect increases considerably.
The distribution of current over the entire cross-section of the conductor is quite uniform in the case of a DC system.
But in the alternating current system, current tends to flow with higher density through the surface of the conductors (i.e., the skin of the conductor), leaving the core deprived of current.
Factors affecting skin effect in transmission lines are:
Frequency – The skin effect increases with the increase in frequency.
Diameter – It increases with the increase in the diameter of the conductor.
The shape of the conductor – Skin effect is more in the solid conductor and less in the stranded conductor because the surface area of the solid conductor is more.
Type of material – Skin effect increase with the increase in the permeability of the material (Permeability is the ability of the material to support the formation of the magnetic field).
Important Points:
The Skin effect is negligible if the frequency is less than the 50Hz and the diameter of the conductor is less than the 1cm.
In the stranded conductors like ACSR (Aluminium Conductor Steel Reinforced) the current flows mostly in the outer layer made of aluminum, 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 an ACSR conductor.
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