Proximity Effect

 Proximity Effect occurs in high A.C. Voltage transmission lines. It occurs two or more overhead conductor due to flux linkages.

When two or more conductor are in proximity, their electromagnetic field interact with each other, with the result that the current in each of them is redistributed such that the greater current density is concentrated in that part of the strand most remote from the interfering conductor. In each case, a reduced current rating results from the apparent increases of Resistance.

Apart from the skin effect the non uniformity of the current distribution is also caused by proximity Effect.Proximity effect is more in case of power cables.

 Let's take a case, Two conductors; current flows in same direction:

Fig. Current flow same direction

We know that, Φ = LI

 It's mean flux is directly proportional to inductor.

 Inductive reactance (XL) = 2πfL

    We can write, L =  XL / 2πf

Now, we can says that, inductor is inversely proportional to frequency.

Conditions:

1.) When supply frequency increases then, proximity Effect increases. It's mean no Proximity occurs in D.C transmission lines.

2.) While Relative permeability increases; proximity Effect increases.

3.) If size of Conductor is increases then proximity Effect occurs.

Method to reduces proximity Effect:

1.) Diameter should be minimum. 

2.) Increasing the distance between the two conductor. 

3.) Reducing the frequency and increasing the voltage we can reduce the proximity effect. 

4.)Always use stranded conductor.