When conductor carries alternating current, it constantly produces alternating magnetic flux around it. This alternating magnetic flux induces circulating currents in the adjacent conductors. In simple words, when two or more conductors are placed close to each other, alternating flux in each conductor is produced by the nearby current carrying conductor. Induce eddy currents↗ increases the resistance of wire which results in more power losses in the system. We can define proximity effect as:
“Proximity effect occurs in alternating current carrying conductor due to the presence of magnetic field generated by another nearby current carrying conductor“. This effect occurs in high A.C. Voltage transmission lines.
Direction and distribution of Current during Proximity Effect:
This effect also cause changings in the current distribution of adjacent conductors. Internal current in both conductor’s flow in undesirable patterns due to the presence of magnetic field generated by the nearer conductor.
Direction of Current is Same :
Consider the situation in which the current in the nearby conductors flows in the same direction. In that case, setup magnetic flux in both adjacent conductors cancel the effect of each other. Since current density in a conductor depends on the magnetic flux distribution. Hence density of current in a conductor on the side facing the nearby conductor is less as compare to the other end. In simple words, current is concentrated in the farthest side of adjacent conductors (see the below fig.).
Direction of Current is Opposite :
If current in the nearby conductors flows in the opposite direction, the magnetic flux of conductors will cause an increase in the current density of adjacent side of conductors. Hence current in that case is concentrated in the nearest side of adjacent conductors ( See the below fig.).
Disadvantages of Proximity effect :
This effect increases the resistance of conductor due to which overall current carrying capacity of conductor is reduced. Moreover, additional resistance increases power losses in the system.
Factors affecting the Proximity effect :
Proximity effect increases with the increase in supply frequency. The magnitude of this effect is very small in case of normal supply frequencies (50 Hz). Since frequency of dc current is zero, hence proximity effect is absent in case of dc currents.
Proximity effect increases when the spacing between the conductors is small.
If conductor is made up of high ferromagnetic material, the effect increases.
How to reduce Proximity Effect ?
The effect can be reduced by increasing the distance between adjacent conductors.
Reducing the frequency and increasing the voltage can also reduce this effect.
Since current is concentrated in the smaller region of conductor due to which resistance is increased. Therefore it is always advisable to use stranded conductor in high voltage AC transmission lines. Stranded conductors increases the surface area for the flow of current which will reduce the resistance of wire( Since resistance and cross sectional area of conductor is inversely proportional to each other ( R=rho L/A). Hence proximity effect reduces.