电力线谐波辐射在分层各向异性电离层中的传播特点

电力线谐波辐射特指在电离层或磁层中观测到的来源于地面电力系统输电线的电磁波辐射, 其在电磁场时频功率谱中表现为400 Hz至5 kHz范围内, 频率间隔为50/100 Hz或60/120 Hz 的平行谱线, 已成为近地空间环境的一种人为污染源. 对于该现象的形成机理尚缺乏定量研究. 本文研究了非理想导电大地上方由电偶极子源产生的电磁场在分层各向异性电离层中的传播模型, 提出了一种新的求解方法, 有效解决了编程计算中的数值溢出问题, 并利用已有解析解对所提方法进行了验证. 在此基础上, 利用实际电力线、大地、电离层的相关参数, 研究了偶极子源频率、电离层下边界高度、大地电导率、地磁场方向等对电力线谐波辐射在电离层中的传播的影响. 结果表明, 频率等于地-电离层波导导波模截止频率时透入电离层的电力线谐波辐射强度更大; 谐波电流一定时, 大地电导率小的地区, 电力线谐波辐射的功率更大; 电力线谐波辐射在电离层中沿地磁场方向传播. 本文所得结果有益于阐释电力线谐波辐射现象的形成机理.

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

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.