Determination of Harmonic Interference Voltages Induced in Paired-Cable Communications Circuits by Harmonic Currents in Adjacent Power Lines

Magnetic field patterns under typical configurations of distribution lines due to harmonic currents are analyzed. Laboratory measurements of differential voltages induced in a section of twisted-pair telephone cable in the presence of known magnetic fields at harmonic frequencies are reported. These data are used to predict induced voltages in communications circuits as functions of harmonic current and distances over which the power and communications cables run parallel. Such results permit much closer estimates of the likelihood of harmful interference for specific circuit configurations than use of the telephone influence factor method.