Skin Effect & Proximity Effect | GATE Notes & Videos for Electrical Engineering - Electrical Engineering (EE) PDF Download

What Is Skin Effect?

When an Alternating Current flows through a conductor, it is not distributed uniformly throughout the conductor cross-section. AC current has a tendency to concentrate near the surface of the conductor. This phenomenon in alternating currents is called as the skin effect. Due to the skin effect, current is concentrated between the outer surface of the conductor and a level called as the skin depth (skin depth is shown by ẟ in the following figure). If the frequency of AC current is very high, the current is restricted to a very thin layer near the conductor surface. Skin effect increases with increase in the frequency.

Due to skin effect, the effective cross-section of the conductor through which the current flows is reduced. Consequently, the effective resistance of the conductor is slightly increased.

Skin Effect & Proximity Effect | GATE Notes & Videos for Electrical Engineering - Electrical Engineering (EE)

The Cause Of Skin Effect

Imagine a solid conductor split into a large number of strands, each strand carrying a small part of current. The inductance of each strand will vary according to its position. Strands located at the center would be surrounded by a greater magnetic flux and, therefore, will have a larger inductance than those near the surface. Higher inductance (and hence, higher reactance) of the inner strands causes the alternating current to flow through the strands having lower reactance, i.e. near the surface.

The skin effect depends upon the following factors:

  • Conductor material: Better conductors and ferromagnetic materials experience higher skin effect
  • Cross-sectional area of the conductor: skin effect increases with increase in the cross-sectional area
  • Frequency: increases with increase in the frequency
  • Shape of the conductor: skin effect is lesser for stranded conductors than solid conductors

Proximity Effect

When two or more conductors carrying alternating current are close to each other, then distribution of current in each conductor is affected due to the varying magnetic field of each other. The varying magnetic field produced by alternating current induces eddy currents in the adjacent conductors. Due to this, when the nearby conductors carrying current in the same direction, the current is concentrated at the farthest side of the conductors. When the nearby conductors are carrying current in opposite direction to each other, the current is concentrated at the nearest parts of the conductors. This effect is called as Proximity effect. The proximity effect also increases with increase in the frequency. Effective resistance of the conductor is increased due to the proximity effect.

Skin Effect & Proximity Effect | GATE Notes & Videos for Electrical Engineering - Electrical Engineering (EE)

Skin effect and proximity effect both are absent in case of DC currents, as frequency of DC current is zero.

The document Skin Effect & Proximity Effect | GATE Notes & Videos for Electrical Engineering - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course GATE Notes & Videos for Electrical Engineering.
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FAQs on Skin Effect & Proximity Effect - GATE Notes & Videos for Electrical Engineering - Electrical Engineering (EE)

1. What is skin effect in electrical engineering?
Ans. Skin effect refers to the phenomenon where alternating current tends to concentrate on the outer surface of a conductor, rather than being evenly distributed across the entire cross-section. This occurs because at high frequencies, the magnetic field generated by the current induces an opposing current in the conductor, which in turn creates a magnetic field that opposes the original current. As a result, the current density is higher near the surface, leading to increased resistance and higher power losses.
2. How does skin effect impact the performance of electrical conductors?
Ans. Skin effect increases the effective resistance of a conductor, leading to increased power losses and reduced efficiency in high-frequency applications. It can also cause a non-uniform distribution of current, which may result in uneven heating and potential damage to the conductor. Additionally, skin effect can affect the impedance and inductance of a conductor, impacting the overall performance of electrical circuits and systems.
3. What factors influence the severity of skin effect?
Ans. The severity of skin effect is influenced by several factors, including the frequency of the alternating current, the resistivity of the conductor material, the cross-sectional area of the conductor, and the geometry of the conductor (such as the shape and surface roughness). Higher frequencies, higher resistivities, smaller cross-sectional areas, and irregular conductor geometries tend to exacerbate the skin effect.
4. What is proximity effect in electrical engineering?
Ans. Proximity effect is another phenomenon that occurs in conductors carrying alternating current. It refers to the tendency of magnetic fields generated by adjacent conductors to interact with each other, resulting in a non-uniform distribution of current within the conductors. This effect is more pronounced at high frequencies and can lead to increased losses and impedance in multi-conductor systems.
5. How can skin effect and proximity effect be minimized or mitigated?
Ans. To minimize skin effect, conductors can be designed with larger cross-sectional areas, which reduce the relative impact of the current crowding near the surface. Another approach is to use hollow conductors or stranded conductors, which provide multiple paths for the current and help to distribute it more evenly. Proximity effect can be reduced by spacing the conductors further apart or using shielding techniques to minimize the magnetic field coupling between adjacent conductors. Additionally, using materials with lower resistivity can also help mitigate both skin effect and proximity effect.
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