Xi = 2π f L
In the case of a transmission line alone; the lower frequencies are the more desirable, in that they tend to reduce the inductance drop and charging current. The inductance drop is proportional to the frequency.
The natural period of a line, with distributed inductance and capacity, is approximately given by
P = 7,900 / √LC
where L is the total inductance in millihenrys, and C, the total capacity in micro-farads. Accordingly some lower odd harmonic of the impressed frequency may be present which corresponds with the natural period of the line. When this obtains, oscillations of dangerous magnitude may occur. Such coincidences are less likely with the lower harmonics than with the higher.
Skin Effect.—The tendency of alternating current to confine itself to the outer portions of a conductor, instead of passing uniformly through the cross section, is called skin effect. The effect is proportional to the size of the conductor and the frequency.
Ques. What effect has "skin effect" on the current?
Ans. It is equivalent to an increase of ohmic resistance and therefore opposes the current.
