Before taking this effect we should remember one is electromagnetic induction. i.e all electrical AC motors are running under this principle. The current carrying conductor creates magnetic flux, upon the magnetic flux cut by a conductor means the current starts flowing. The same effect in the transmission and distribution line is called proximity effect. The alternating magnetic flux in a conductor caused by the current flowing in a neighboring conductor gives rise to circulating currents which cause non-uniformity of current and increases the apparent resistance of the conductor. This effect is called Proximity effect.
Let us consider, two wire A and B. here when the current flow in the A conductor which magnetic flux cut but the conductor B. The flux linkages are nearer to the conductor A. i.e the shaded portion than the opposite side of B. if the current in the conductor B is opposite to the current in A, the current density will be more in the adjacent portion of the conductor. Due to this, the effective resistance of AC is more than that of DC.
Proximity Effect is negligible in transmission lines because the distance between the conductor is high. and but in case of cable where the conductors are nearer to each. It is depending upon the size of the conductor, frequency, resistivity and permeability of the material.
How Reduce Proximity effect:
- Reducing the size of the conductor
- Increasing the distance between the two conductor. I.e in cable manufacturing to reduce increase the distance between the conductor, we use dummies.
- Reducing the frequency and increasing the voltage we can reduce the proximity effect. It is practically not possible. However, AC frequency cannot be changed. But we can step up the voltage further steps.