Propagation characteristics of power line harmonic radiation into the stratified anisotropic ionosphere

Abstract

Power line harmonic radiation (PLHR), which specifically refers to the electromagnetic wave radiation observed in ionosphere or magnetosphere, is radiated by the transmission lines of power systems on the ground. PLHR is shown as a parallel spectrogram between 400 Hz and 5 kHz in frequency-time power spectrogram of electromagnetic field. And the frequency spacing of the parallel spectrogram is 50/100 Hz or 60/120 Hz. As an artificial pollution source in the near earth space, PLHR has attracted more and more attention. However, so far, there have been little proposed quantitative researches on the formation mechanism. This paper studies the propagation model for the electromagnetic waves generated by the electric dipole source above the non-ideal conductive ground in the stratified anisotropic ionosphere. Based on the method by Lehtinen(2008), a new full-wave finite element method is give to solve the problem. By recursively calculating reflection coefficients and mode amplitudes, the method contains no index increasing items. So it can effectively overcome the numerical overflow in programming calculations. In order to verify the correctness of the method, comparison are made between the existing analytical solutions and the solutions obtained from the proposed method, and they are in excellent agreement. Further more, using the present model, the new method and the associated parameters about practical power lines, ground and ionosphere, we have studied the effects of the frequency of dipole source, the bottom boundary height of ionosphere, the earth conductivity, and the geomagnetic field direction on PLHR propagation in the ionosphere. Results show that when the frequency of radiation source equals the cut off frequency of earth-ionosphere waveguide-guided wave modes, the strength of PLHR for penetrating into the ionosphere becomes larger. Keeping the harmonic current constant, a smaller ground conductivity would be accompanied by a larger power of PLHR. PLHR propagates along the direction of the geomagnetic field in the ionosphere. Therefore, it is much easier for a high-order harmonic radiation of transmission lines to penetrate into the ionosphere along the direction of the geomagnetic field in the areas with low ground conductivity under a certain condition. Results obtained in this paper may have important implications to explain the formation mechanism of PLHR.