Skin Effect, Ferranti Effect Tutorial

Introduction to Skin Effect and Ferranti Effect

Skin Effect: Basics, Causes, Factors, Reduction

When a conductor carries steady current ie, direct current the current density throughout that conductor will be uniform. But while AC current flow through the conductor it will not be true, rather it has a tendency to concentrate near the surface of the conductor. This phenomenon is called as skin effect.

Definition:

The tendency of alternating current to concentrate near the surface of the conductor is known as skin effect.

Causes for skin effect:

  • A solid conductor, assumed to be consisting of large number of strands each carrying a small part of the current.
  • The inductance of each  part of the strand varies depending on its position.
  • Thus strands near the centre are surrounded by a greater magnetic flux having large inductance than at the surface.
  • The high reactance of linear strands cause the AC current to flow near the surface of the conductor.
  • The effective area of the cross-section of the conductor is reduced due to this skin effect.

The skin effect will be higher with

      1. The frequencies more than 50Hz.
      2. The size of the conductor is more than 1cm2

Factors affecting Skin effect:

The skin effect depends upon the following factors:
(1) Diameter of the wire
When the diameter of the conducting wire increased the skin effect will increase drastically.
The skin effect is negligible when the diameter of the wire is less than 1cm.
(2) Frequency
The skin effect is directly proportional to the supply frequency ( ie, increases with the frequency).
The skin effect is negligible when the frequency is less than 50Hz.
(3) Shape of wire
To minimize the skin effect, the shape of the  wire should be less for stranded conductor than that of solid conductor.
To reduce the skin effect, stranded conductors are used in transmission and distribution lines.
(4) Nature of material

Ferranti Effect:

                      When the long transmission line with high capacitance is unloaded or it is operated at light loads it will be observed that the voltage the receiving end is more than that of the sending end. This phenomenon of rise of voltage at the receiving end during lightly loaded or unloaded line is called as Ferranti effect.

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