Abstract：A large amount of satellite-based observations show that the radiation corresponding to the power grid harmonic frequencies with the strength of more than 10dB greater than background noise exits in the near-Earth space. Some references believe that it is originated from power lines and name it power line harmonic radiation (PLHR). This paper studies the specific source of the power grid corresponding to PLHR by comparing the ground-based measurements with the satellite-based measurements and discusses its propagation mechanism in the ionosphere The spectrogram of the electric field strength observed along satellite DEMETER orbits that point in the same general direction as the Jindongnan-Nanyang-Jingmen ultra-high voltage (UHV) AC transmission line has been analyzed first. The results show after the UHV project went into operation at the end of 2008, the number of PLHR events in the frequency range of 2~5 kHz occurring in the ionosphere increased sharply. The ground-based measurement results show that the harmonic radiations at 2.5~3 kHz and 4~4.5 kHz do exist at the head end of the UHV project. The above results indicate the source of PLHR is closely connected with the UHV project. The full-wave model is used to explore the propagation characteristics of the UHV project's electromagnetic wave in the ionosphere. A horizontal dipole with the length of 200 m and the height of 12 m above the ground is used to equivalent the harmonic radiation source and the ionosphere is regarded as a stratified, linear, anisotropic and uniform plasma. The numerical results show that the electric field strength reaches the maximum values 0.15 μV/m of 2.8 kHz at (660 km, 530 km) in which 660 km is the altitude of DEMETER and 530 km is the distance away from DEMETER in the horizontal direction and 0.07 μV/m of 4.25 kHz at (660 km, 540 km), respectively. These values are close to but generally lower than the electric field strength of 0.09~0.27 μV/m observed by DEMETER which is 551 km away from the UHV line in the horizontal direction. The difference between the theoretical analysis results and satellite-based measurement results indicates that there is a nonlinear amplification physical process during the propagation of PLHR in the ionosphere. The propagation mechanism of very low frequency waves between the North-South geomagnetic conjugate regions is then investigated to explain the propagation mechanics of PLHR. The propagation path of the wave in the ionosphere follows Snell's law. Lower hybrid frequency fLHF is the critical frequency that only those waves with the frequencies below it can propagate between the hemispheres. fLHF is calculated as 4.9 kHz by using the electron density and ion density observed by the satellite. The frequencies of all detected PLHR events are below fLHF, indicating that PLHR might theoretically cross the equator and propagate to the conjugate hemisphere. This procedure enables PLHR to be enhanced near the equator. Actually, PLHR events at approximate 4 kHz have been detected over the UHV project and its conjugate region near western Australia and the strength of events at the southern hemisphere is close to or even larger than that at the northern hemisphere, but the radiations at approximate 50 Hz have been detected only over the UHV project. Due to the complexity of the ionospheric plasma environment, it is challengeable to figure out the formation mechanism of PLHR and its resulting electromagnetic effects at present. However, with the development of UHV power transmission and transformation projects, its resulting radiations in the near-Earth space deserves more attention.
张敬雯, 吴静, 谢天宇. 近地空间与电网相关的谐波辐射现象研究[J]. 电工技术学报, 2023, 38(11): 2861-2869.
Zhang Jingwen, Wu Jing, Xie Tianyu. Research on Harmonic Radiation Related to the Power Grid in the Near-Earth Space. Transactions of China Electrotechnical Society, 2023, 38(11): 2861-2869.
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2023, Vol. 38 
