The proximity effect in transmission lines is a phenomenon that occurs when conductors carrying alternating current are too close together, causing a non-uniform current distribution in the transmission line and increasing the conductors apparent resistance). The proximity effect is caused by the varying magnetic field produced by alternating current, which induces eddy currents in adjacent conductors. The effect is more pronounced at higher frequencies and is influenced by factors such as conductor material, conductor diameter, frequency, and conductor structure. The proximity effect can be reduced by reducing the size of the conductor and the frequency, increasing the voltage and space between conductors, and using stranded conductors instead of solid conductors. The proximity effect can cause power loss and voltage drop along the transmission line, which can be mitigated by implementing changes to reduce the effect.