Power Line Carrier Coupling Investigations on a 500-kV Line

Some previously accepted concepts of power line carrier coupling do not apply on power lines with very few transpositions. For such lines, the attenuation and impedance of the carrier circuit may be strongly dependent on which phase conductor is selected for coupling. This phenomenon has been investigated in a series of tests on a long 500-kV line with one transposition near the middle. The results, which are explained in terms of the modal propagation theory, show a difference of as much as 15 dB in attenuation at certain frequencies between the optimum and a more conventional form of carrier coupling.