Skin Effect Experiment

INTRODUCTION

Skin effect is a phenomenon common to every electrical conductors carrying alternating current (AC) in which the distribution of the AC across the conductor’s cross section is such that the current density near the surface is largest and decreases as the depth increases into the conductor’s core. This means the AC only flows principally across the area of the conductor known as skin between the surface and a depth termed the skin depth. This skin depth effectively poses restriction to the flow of electric current which ultimately increases the overall resistance of the conductor and decreases the internal inductance. The resistance is more pronounced with frequencies causing the skin depth to be smaller and thus decreasing the

Constituting the current are charge carriers which are electrons driven by an electrical field as a result of the electrical energy source. This AC in the conductor induces an alternating magnetic field around and in the conductor, and the magnetic field changes as the AC intensity in the conductor changes. This change in the magnetic field also induces an electric field which in turn opposes the change in current intensity. The opposing electric field is called back electromotive force and this is very intense at the centre of the conductor and then pushes the charge-carrying electrons to the surface of the

d = distance measured from the surface toward the center of the conductor s_d = skin depth

Figure 1 shows the effect of skin effect on the current density from the surface of the conductor to the centre and the case of uniform current density.

As defined above, the skin depth can be calculated as below: q=q_o⁄e Figure 1 Uniform Current Density and Skin Effect Impact

Mitigation

This increased resistance to the flow of electric current caused by skin effect can be mitigated by the use of some special litz (Germans braided wire called Litzendraht) which consist of special insulated wire strands formed together in a unique pattern. The aim of this is to ensure that the magnetic field acting on the wires is equal thereby causing the current flowing through them to be equally distributed. The litz wire is often used in transformers to increase their