The skin effect is a phenomenon that occurs in alternating current (AC) transmission lines, particularly those carrying high-frequency currents. It refers to the tendency of AC current to distribute itself unevenly across the cross-sectional area of a conductor, with the majority of the current flowing near the surface of the conductor rather than uniformly through its entire cross-section. This effect is a result of the electromagnetic field generated by the alternating current.
In AC transmission lines, the current alternates direction at a specific frequency. As the current changes direction, it generates a magnetic field around the conductor according to Ampere's law. This changing magnetic field induces eddy currents within the conductor itself. These eddy currents, in turn, create their own magnetic fields that oppose the original magnetic field.
As the frequency of the AC current increases, the opposing magnetic fields generated by the eddy currents become stronger. This interaction between the original alternating current and the induced eddy currents causes the effective resistance seen by the alternating current to increase. This higher effective resistance leads to the concentration of the current near the surface of the conductor, where it encounters less opposition from the induced magnetic fields.
In essence, the skin effect results in a reduction of the effective cross-sectional area through which the current flows. The current density (current per unit area) is highest at the outermost layer of the conductor and gradually decreases as you move toward the center. This phenomenon leads to increased resistance, which in turn can result in higher power losses and reduced efficiency in the transmission line.
To mitigate the effects of the skin effect, conductors used in high-frequency AC transmission lines are often designed with larger diameters or with multiple smaller strands bundled together. This increases the overall surface area and helps distribute the current more evenly across the conductor, thereby reducing the impact of the skin effect and minimizing energy losses.