“Skin effect” we first split to understand tend: can be understood as the meaning of tendency. Skin: you can use the meaning of “surface”

to understand, and in electricity, here “skinning” is actually: tend to the surface of the meaning, and this surface is the surface of the conductor.

So what exactly tends to the surface of the conductor? The answer is “electrons.”

Alternating current through the conductor, the center of the conductor does not have any current, the current is almost all concentrated to the

surface of the conductor is very thin, very thin layer, this phenomenon is called the “skin effect”, as shown in Figure 1 above on the right.

What is the reason for the skin effect? The fundamental reason is: when the alternating current through the conductor, the conductor center

part of the vortex electric field, hindering the flow of the original current, resulting in most of the electrons are forced to only go to the edge

of the conductor part. Later described in detail.
For the skin effect, some people say: the current is actually just flowing on the surface of the wire, the wire center part of the slow movement of

electrons or even almost no movement, so the wire should be multi-stranded copper wire without a single solid wire.

This may be the current of the “skin effect” there is a general misunderstanding of the bar, multi-stranded wire insulation, if there is no

insulation, to reduce the skin effect does not help.

1 DC and AC magnetic fields
When we apply a voltage at both ends of the wire, the potential difference will form an electric field inside the conductor, which in turn

generates an electric current.

Current is divided into direct current and alternating current, direct current due to the direction of the electric field is unchanged, the

charge in the wire unidirectional movement; alternating current due to the direction of the electric field is a periodic reversal, so the direction

of the movement of the charge in the wire and the intensity of the periodicity of the change.

Whether it is direct current or alternating current, due to the relationship between the movement of the charge, it will produce a magnetic

field inside the wire and around the wire. The direction of the magnetic field produced by direct current is relatively easy to determine,

you can by the right hand grasping rule, the thumb will be aligned with the direction of the current, the other four fingers is the direction

of the electromagnetic field.

The direction of the magnetic field of alternating current is a little more complicated, because the direction and strength of the current

of alternating current is not fixed, so the electromagnetic field generated by alternating current is also constantly changing.
2 Generation of eddy currents

Due to the alternating current field in the wire is constantly turning, the magnetic flux generated by the electric field is also constantly changing,

Faraday’s law tells us that the changing magnetic flux will be induced in the conductor electric potential, this induced electromotive force will

be formed in the conductor inside the ring eddy current.

The induced magnetic field inside the conductor generated by the ring vortex is a changing electric field, its outer and alternating current in the

same direction, and near the wire axis of the region of the formation of the reverse electromotive force, which results in the outer surface of the

conductor is strengthened, while the middle of the current is weakened , it seems that the current are concentrated in the surface of the wire

“skin ”, so we call this phenomenon skin effect, or skin effect.

3 the practical significance of the skin effect

Understanding the current skin effect is of great significance. In the design of high-voltage transmission lines, we can not simply by increasing the

diameter of the wire to obtain a large current, because when the diameter of the copper wire more than 2 cm, it is the center part of the current

is very little, resulting in a waste of materials. In order to transport more power, UHV transmission will use multiple bundles of identical cables to

increase efficiency and reduce losses.

Since DC power generally does not have a varying electric field, it does not produce a varying magnetic field during transmission, so DC power

does not produce eddy currents. DC transmission lines have much lower resistance than AC transmission, it is more energy efficient, and the

cables can be made thicker and correspondingly less costly.

Our household electricity wires are usually not very thick, most of the core diameter of not more than 5 mm, why is it also used in multi-stranded

copper wire? The radius of the household wire is much smaller than the skin depth of 9.2 mm, basically do not need to consider the skin resistance,

and these thin copper wires are not insulated from each other, which does not help to reduce the skin effect. The main reason for using multi-stranded

copper wire is that it is softer than single stranded copper wire for the same cross-sectional area.