[2023] All About The Skin Effect Explained in Detail

    When ac current passing through a conductor is observed, it is found that the majority of the current will flow from the outer part or skin or surface of the conductor. This phenomenon of uneven distribution of alternating current through-out the cross-section of the conductor is known as skin effect. It mean that more ac current is flowing near the outer part or  surface or skin of the conductor and decreases exponentially as towards the core. Hence, outer part of a conductor carries more ac current than inner part that increases effective resistance of the conductor.

    Skin effect reduces the effective cross-sectional area of the conductor available for the current flow resulting increase in power losses and heating of the conductor. Skin effect also causes change in the impedance of the transmission line which affects the voltage and current distribution along the line. Skin effect is mainly occurs in the conductor at higher frequencies, of larger diameters and lower conductivity.

    Skin effect does not occur in direct current (dc) system because frequency is zero in the dc system thus, the dc current flows uniformly through-out the cross-section of the conductor. AC systems especially those that operating at high frequencies such as radio and microwave systems mainly have significant impacts of skin effect on the performance, efficiency, design and analysis of transmission lines and other components of the power system.

Causes of Skin Effect

    Skin effect is caused by the interaction of the magnetic field generated by the ac current flowing through the conductor with the conductor itself. when an ac current flows through a cylindrical conductor, it creates a magnetic field around it inside the conductor. The direction and magnitude of this magnetic field changes as the frequency and amplitude of the ac current changes. A changing magnetic field induces an electric field in a conductor according to the faraday’s law of electromagnetic induction. This electric field induces an opposing current in the conductor called an eddy current that circulates within the conductor opposing the ac current.

    The eddy currents are stronger near the core of the conductor where they have more magnetic flux linkage with the ac current. Hence, they create a higher opposing electric field and reduce the net current density at the core of the conductor. But near the surface of the conductor, there is less magnetic flux linkage with the ac current, there are weaker eddy currents and a lower opposing electric field. Hence, there is a higher net current density at the surface of the conductor.

    In short, uneven linkage of magnetic flux through-out the cross-section of the conductor results uneven distribution of ac current through-out the cross-section is major cause of skin effect.

Factor Affecting Skin Effect

    The factors that affects the skin effect has been listed below.

1. Supplied Frequency :- Skin effect is directly proportional to the frequency i.e it increases with increase in frequency.
2. Diameter of the Conductor :- Skin effect is directly proportional to the diameter of the conductor i.e it increases with increase in the diameter of the conductor.
3. Type of material of the conductor :- Skin effect is more in the solid conductor and less in the stranded and hollow conductors.
4. Nature of Material used :- Skin effect is directly proportional to the relative permeability i.e  it increases with increase in relative permeability of the material used as relative permeability supports the formation of magnetic field.
5. Temperature of the Conductor :- Skin effect is directly proportional to the temperature of the conductor i.e it increases with increase in temperature of the conductor as increase in temperature increases the size of the conductor i.e diameter increases.

Skin Depth of a Conductor

    Skin depth is one way to quantify skin effect. Skin depth is defined as the depth below the surface of the conductor at which current density falls to 1/e times (i.e about 37%) of its initial value. The smaller the skin depth, more serve the skin effect.

Disadvantages of Skin Effect

    The disadvantages of the skin effect has been listed below.

1. Effective cross-sectional area reduced and effective resistance increases.
2. Power loss increases as copper losses and heat loss increases
3. Voltage drop increases resulting poor voltage regulation
4. Efficiency and reliability of the system is reduced

Methods to Reduce Skin Effect

There are some methods that can be used to reduce the skin effect which are listed below.

1. By using stranded conductor :- Stranded conductor consists of several thin wires of small cross-section aligned as a single conductor which is flexible than solid conductor and reduces the skin effect.
2. By using hollow conductor :- Hollow conductor is used to reduce the material and cost of the conductor as majority ac current flows through the outer part or surface of the conductor.
3. Reducing the diameter :- Skin effect can be reduced by reducing the thickness of the conductor.
4. By increasing conductivity :- Skin effect can be increased by using the conductor of high conductivity.
5. By reducing permeability :- Skin effect can be reduced by using the conductor of low permeability.
6. By using parallel conductors :- Skin effect can be reduced by using multiple parallel conductors instead of a single conductor as it increases the effective cross-sectional area of the conductor and reduces the effective resistance.
7. By reducing frequency :- Skin effect can be reduced by reducing the frequency of the ac current as it increases the skin depth.

References

• electrical4u.com
• circuitglobe.com
  
• electricalpaathshala.com
  
• wikipedia.org