A Study on Basic Characteristics of the Proximity Effect on Conductors

The basic and qualitative characteristics of the proximity effect in comparison with the skin effect on multiconductors are investigated based on finite-difference time-domain simulations to find equivalent/approximate geometrical parameters by which a transient can be calculated by existing electromagnetic transients-type simulation tools. The proximity effect appears very different depending on the current directions on the conductors, and is cancelled out in the center conductor on a three-conductor system. A filament current assumption results in a quite different current distribution from that considering the conductor volume. Based on the investigation and the IEC formula, an approximate formula of the conductor impedance considering the proximity and skin effects is proposed. The validity of the proposed formula is confirmed by calculated results of the impedance compared with the IEC formula, and of an intersheath mode transient in comparison with a field test result. The formula makes it possible to calculate a transient with the proximity effect by the EMTP.