Proximity Effect and Skin Effect

Proximity Effect and Skin Effect, Electrical Dost

Proximity Effect

As seen above, the “skin effect”, we have considered the flux of the conductor only But there is another conductor line near to it carrying current. Then its flux will also link with the first conductor and its effect to the nearer half of the conductor will be more than the back half of the conductor. Similar to the skin effect, this affects current distribution and ultimately the effect is to increase the resistance of the conductor and to decrease the self reactance. Moreover, power loss increases due to this effect. Two conductors A and B are near to each other but a distance’ apart.

Proximity Effect and Skin Effect, Electrical Dost
Fig.1. Proximity Effect

When conductor ‘A” carries A.C. current, its flux links with B and half of the portion of B facing A (Shown shaded) has more flux linking than back half (unshaded).

Proximity effect depends on:

1) Frequency and is proportional to frequency.
2) Increases With the increase in the diameter of the conductor.
3) Less for stranded shape rather than solid shape.
4) Type of material (1.e. resistivity (P) of conductor material and permeability of material).

Skin Effect

The tendency of the alternating current flow to be Concentrated near the outer surface of a conductor and as it, no current in the central portion of the conductor is called “skin effect”.

Proximity Effect and Skin Effect, Electrical Dost
Fig.2. Skin Effect

In the case of D.C., the current is uniform through the cross-section, hence there is no skin effect in D.C.

Proximity Effect and Skin Effect, Electrical Dost
Fig.3.

Think, that a solid conductor is consisting of small circular strands in circular C.S. of solid conductor and each strand is carrying a small part of alternating Current. The strands near the center are surrounded by a greater magnetic flux in comparison with outer are strands, and inductance and, hence inductive resistance (&) of the inner portion is greater than the outer portion. Hence, the inner portion offers more opposition to current and forces the current to the outer surface and hence current al central portion is very small and current flow concentrates on the outer portion i.e. near and on the surface of the solid conductor. This is “‘skin effect”.
In D.C., the changing flux is absent hence XL does not come into the picture.
So skin effect in not present in the case of D.C.

Skin effect depends on:

This effect depends on (Note: Skin effect and proximity effect depending on similar lines)
1) Frequency and is proportional to frequency.
2) Increases With the increase in the diameter of the conductor.
3) Less for stranded shape rather than solid shape.
4) Type of material (1.e. resistivity (P) of conductor material and permeability of material).

These two effects are negligible for small size, small current-carrying conductors but predominant in case of big size conductors carrying bulk currents. While calculating the resistance of the transmission line, the skin effect and proximity effect should be considered.

The explanation of the effect of a rise in temperature

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