Study of the frequency response of the mutual coupling between overhead lines

The paper investigates the frequency response of the mutual coupling between multi-wire overhead lines with length comparable to the wavelengths of the highest power frequency harmonics. Deenergized overhead transmission lines are influenced by electromagnetic interference from neighboring in-service overhead lines, railway traction lines, as well as other extended conductors with currents. The voltages induced on the overhead lines are dangerous to life or health of maintenance personnel. The values of the induced voltages can be determined either by direct measurement or by calculation. The paper presents the results of experimental studies of double-circuit overhead lines of the Kola energy system. It has been shown that the frequency spectrum of the induced voltage is different from the spectrum of the source of interference, and this difference has a resonant nature. The amplitude of the voltage induced by higher harmonics can be comparable with the amplitude of the voltage induced by the power frequency. The similar results have been received in studies of influence of the AC railway traction line on adjacent overhead transmission lines. ATP-EMTP numerical analysis has been performed to receive the frequency characteristics that explain the experimental results. Preliminary estimates indicate that the cause of the phenomenon is most likely due to the resonant nature of the frequency response of the mutual coupling. The resonant nature is characterized by the interrelation of the length of overhead lines and the wavelength of the higher harmonics. A wave resonance of currents and voltages that appears in the lines lead to the "magnification" of the individual induced voltage harmonics falling in the maxima of the frequency characteristics of mutual coupling.