Power Line Harmonic Radiation Research Articles

Conjugate observations of power line harmonic radiation onboard DEMETER

The effects of power line harmonic radiation (PLHR) on near-Earth space have been debated for many years. Since some ultrahigh voltage AC and DC power projects were added to the Chinese power grid, increasingly numerous radiations at 50 Hz and their harmonics have been caught by the microsatellite DEMETER in the geomagnetically conjugate topside ionosphere during the daytime of winter and spring. Distribution of SYM-H index has been studied, showing geomagnetic disturbances may be unnecessary for the occurrence of PLHR. The propagation of PLHR between hemispheres without much attenuation illustrates that PLHR can be amplified when crosses the equatorial zone. Eliminating seasonal and diurnal factors, dependence of PLHR propagation on the change in plasma density is disclosed. The abrupt variation of electron density gradient may create a favored condition for PLHR waves propagating between hemispheres.Graphical

CSES Satellite Observations of 50 Hz Power Line Radiation Over Mainland China and Its Response to COVID‐19

AbstractWe present a low‐altitude satellite survey of power line harmonic radiation (PLHR) at 50 Hz over Mainland China. We analyzed the month‐to‐month variation pattern in PLHR occurrence rate and further analyzed its correlation with some influencing factors (i.e., solar radiation, lightning flashes, and electricity consumption) using CSES satellite electric field data from 2019 to 2021. We also investigate the response of PLHR occurrence rate to COVID‐19. The statistical results show the dayside PLHR occurrence rate decreasing from winter to summer solstice and increasing from summer to winter solstice, which indicates it is controlled by the solar radiation. The nightside variation is more complex, which may be due to many sources that could influence the nightside lower ionosphere. The PLHR occurrence rate significantly decreased over Mainland China in February 2020, which is because of the significant decrease in electricity consumption due to the suspension of industrial production caused by COVID‐19.

Power Line Harmonic Radiation Observed by the Van Allen Probes Spacecraft

AbstractWe present a systematic analysis of Power Line Harmonic Radiation (PLHR) electromagnetic wave events observed by the Van Allen Probes spacecraft over the entire duration of the mission (2012–2019). PLHR events are radiated by electric power systems on the ground at harmonics of the base power system frequency (50 or 60 Hz, depending on the region). We analyze wave intensities at frequencies corresponding to the first few harmonics and we demonstrate that they are significantly enhanced at the times when the field‐aligned magnetic footprint of the spacecraft is above industrialized areas. Considering the spacecraft locations close to the equatorial plane, this represents experimental evidence that PLHR emissions may propagate up to radial distances as large as about 4 Earth radii. Average frequency spectra above selected industrialized regions reveal increased wave intensities at the frequencies corresponding to the first and the third harmonics, in particular during the nighttime. Multicomponent wave measurements allow us to perform a detailed wave analysis of polarization and propagation properties of the events. The waves are typically right‐handed elliptically or nearly circularly polarized, propagating with oblique wave normal angles from low latitude sources and more field‐aligned wave vectors from high latitude sources. The sign of the parallel component of the Poynting flux confirms that the events indeed propagate from the anticipated ground regions. Few events observed above the United States region propagate in the opposite direction, which is interpreted as wave bouncing between the hemispheres.

On the use of ELF/VLF emissions triggered by HAARP to simulate PLHR and to study associated MLR events

A spectrogram of Power Line Harmonic Radiation (PLHR) consists of a set of lines with frequency spacing corresponding exactly to 50 or 60 Hz. It is distinct from a spectrogram of Magnetospheric Line Radiation (MLR) where the lines are not equidistant and drift in frequency. PLHR and MLR propagate in the ionosphere and the magnetosphere and are recorded by ground experiments and satellites. If the source of PLHR is evident, the origin of the MLR is still under debate and the purpose of this paper is to understand how MLR lines are formed. The ELF waves triggered by High-frequency Active Auroral Research Program (HAARP) in the ionosphere are used to simulate lines (pulses of different lengths and different frequencies). Several receivers are utilized to survey the propagation of these pulses. The resulting waves are simultaneously recorded by ground-based experiments close to HAARP in Alaska, and by the low-altitude satellite DEMETER either above HAARP or its magnetically conjugate point. Six cases are presented which show that 2-hop echoes (pulses going back and forth in the magnetosphere) are very often observed. The pulses emitted by HAARP return in the Northern hemisphere with a time delay. A detailed spectral analysis shows that sidebands can be triggered and create elements with superposed frequency lines which drift in frequency during the propagation. These elements acting like quasi-periodic emissions are subjected to equatorial amplification and can trigger hooks and falling tones. At the end all these known physical processes lead to the formation of the observed MLR by HAARP pulses. It is shown that there is a tendency for the MLR frequencies of occurrence to be around 2 kHz although the exciting waves have been emitted at lower and higher frequencies.Graphical

Special Electromagnetic Interference in the Ionosphere Directly Correlated With Power System

Power line emissions and harmonic radiations have been recognized as a kind of electromagnetic interference to the near-Earth space environment. This study demonstrates their direct dependence on the terrestrial power system used. By examining electric field data obtained by the satellite DEMETER, we observed several typical 50-, 60-, and 180-Hz emissions above Japan originating from a 50-Hz/60-Hz hybrid power system over two consecutive days. We analyzed all the emission events of 50 Hz and its harmonic frequencies detected as DEMETER flew over China. In 2009, the number of power line harmonic radiation (PLHR) events suddenly increased when multiple ultra-high-voltage transmission lines were built and put into operation. Based on the seasonal and diurnal distribution of the observed events, we conclude that PLHR is closely related to power consumption as we observe that it is mainly distributed above highly populated places and as such the radiation may originate from the low-voltage power distribution network. The magnitude and frequency of electrical currents flowing through transmission lines during both regular and faulty operation that can generate emissions reaching the ionosphere are analyzed for different voltage classes.

Correlation Between Power Line Harmonic Radiation and Magnetospheric Line Radiation Over China

Power line harmonic radiation (PLHR) and magnetospheric line radiation (MLR) are recognized as electromagnetic pollutants in the near-earth space, and their correlation has been a controversial issue. An identification procedure based on short-time discrete Fourier transform and Welch power spectrum estimation was applied to detect 114 PLHR events and 328 MLR events that occurred as DEMETER satellite flew over China from 2008 to 2010. PLHR events feature parallel horizontal lines with a frequency interval of 50/100 Hz in spectrogram, whereas MLR events feature multi-parallel spectral lines with frequency drift as a baseline for possible triggered emissions as well as triggered emissions with no baseline. We statistically compared the temporal and geographical distribution, Kp and Dst indices, and propagation characteristics between PLHR and MLR events. PLHR events showed more obvious variations annually than MLR events, and the former had a close relationship with the development of Chinese power system. Both PLHR and MLR presented similar diurnal and seasonal differences, owing likely to the ionospheric state; moreover, they appeared to have no significant connection with geomagnetic activity level. The geographical distributions of PLHR and MLR differed significantly. PLHR events occurred in the range of (20° N–45° N), whereas MLR events were concentrated in southwestern low-latitude regions of (18° N–28°N). Furthermore, PLHR waves were right-hand circularly polarized, whereas MLR waves were approximately linearly polarized. In summary, MLR is more likely caused by natural radiation that is not directly related to PLHR, whereas PLHR is closely related to terrestrial power systems.

Theoretical Analysis on Affecting Factors of Power Line Harmonic Radiation

Power line harmonic radiation (PLHR) is an artificial electromagnetic pollution source in the near-earth space environment. Up until now, there has been little quantitative research on its formation mechanism. This paper details a model and solver for electromagnetic waves propagation in a stratified anisotropic ionosphere. In our model, these electromagnetic waves are generated by an arbitrary electric dipole source above a nonideal conductive ground. The matrix-exponent method and a full-wave method are combined to analyze the model, avoiding the problem of numerical overflow and swamping in numerical calculations. The computing results obtained from the proposed method and the observed electric field data by using DEMETER satellite are compared and found to be in good agreement. Furthermore, this paper considers the effects on PLHR propagation in the ionosphere due to dipole source frequency, earth’s conductivity, electron density, geographic latitude, and geomagnetic field orientation. Results show that when the frequency increases, the strength of PLHR penetrating into the ionosphere has an increasing tendency. If the harmonic current remains constant, lower ground conductivity and electron density of the ionosphere result in higher radiation power. PLHR propagates along the direction of the geomagnetic field in the ionosphere, and its strength decreases with the increasing geomagnetic inclination at the same height. In addition, the radiation power of less than 1 W may trigger PLHR.

Influences of radiation from terrestrial power sources on the ionosphere above China based on satellite observation

The environmental effect on the ionosphere caused by man-made power line emission (PLE) and power line harmonic radiation (PLHR) has become an increasing concern. Based on the observed data of 6.5 operating years of DEMETER satellite, by scanning the electric field power density time-frequency spectrograms, 133 PLHR events with central frequencies from 500 Hz to 4.5 kHz are detected in the near-Earth space above China. The fundamental frequency related well to the frequency of corresponding ground power system. Among the 133 events, 129 events have PLE events at the base power system frequency (50 Hz in China). The duration time of every PLE event covers that of the corresponding PLHR event totally. As the same with PLHR, PLE is also propagating in whistler mode in the ionosphere. In two events that are detected in the conjugate region of Australian NWC VLF transmitter, radiations with line structure in the vicinity of 19.8 kHz are detected, suggesting a possible interaction between the NWC signal and radiation from China’s power system.

DEMETER observations of manmade waves that propagate in the ionosphere

Abstract This paper is a review of manmade waves observed by the ionospheric satellite DEMETER. It concerns waves emitted by the ground-based VLF and ELF transmitters, by broadcasting stations, by the power line harmonic radiation, by industrial noise, and by active experiments. Examples are shown including, for the first time, the record of a wave coming from an ELF transmitter. These waves propagate upwards in the magnetosphere and they can be observed in the magnetically conjugated region of emission. Depending on their frequencies, they perturb the ionosphere and the particles in the radiation belts, and additional emissions are triggered.

Systematic investigation of power line harmonic radiation in near‐Earth space above China based on observed satellite data

AbstractThe environmental impact of power line emission and power line harmonic radiation (PLHR) in near‐Earth space has become an increasing concern. In the years 2004–2010, based on the data of microsatellite DEMETER, 133 PLHR events are detected in near‐Earth space above China. PLHR has a close correlation with the development of China's electric power network. Its central frequency appears to depend on the latitude. The geographic distribution of the events occurs in clusters. Several events take place continuously above specific regions. PLHR shows no significant dependence on geomagnetic activity. There are more events in daytime than in nighttime and more in winter than in summer. The differences of naturally generated whistlers and power consumption between day and night and the strong thunderstorms in local summer may lead to such diurnal and seasonal differences of PLHR.

Chorus and chorus‐like emissions seen by the ionospheric satellite DEMETER

AbstractA lot of different emissions have been detected by the low‐altitude satellite DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions), and the aim of this paper is to study extremely low frequency (ELF) electromagnetic waves with elements drifting in frequency. It is shown that only some of them can be considered as usual chorus. These chorus elements are emitted in the equatorial plane, and their propagation analysis indicates that they are going downward at low altitudes in the ionosphere to be detected by the satellite. The study of one remarkable event recorded along the same orbit in both the Northern and the Southern Hemispheres on 8 May 2008 indicates that this propagation mechanism is reinforced at the location of the ionospheric trough, which corresponds to the plasmapause at higher altitudes. It has been observed that usual chorus elements at low frequencies are always in a frequency band which overlaps with a hiss band limited by a frequency cutoff close to the proton gyrofrequency. Other drifting elements can be attributed to emissions triggered by PLHR (power line harmonic radiation). It means that without a high‐resolution spectral analysis, chorus‐like elements triggered by PLHR can be wrongly considered as natural chorus. These drifting elements can also appear as filamentary structures emerging at the upper frequencies of a hiss band or quasiperiodic emissions. There are events where the elements even have certain similarities to quasiperiodic emissions. The difference between these elements and the chorus emissions will be emphasized.

Power line harmonic radiation observed by the DEMETER spacecraft at 50/60 Hz and low harmonics

AbstractWe present a low‐altitude satellite survey of Power Line Harmonic Radiation (PLHR), i.e., electromagnetic waves radiated by electric power systems on the ground. We focus on frequencies corresponding to the first few harmonics of the base power system frequencies (50 Hz or 60 Hz, depending on the region). It is shown that the intensities of electromagnetic waves detected at these frequencies at an altitude of about 700 km are significantly enhanced above industrialized areas. The frequencies at which the wave intensities are increased are in excellent agreement with base power system frequencies just below the satellite location. We also investigate a possible presence of the weekend effect, i.e., if the situation is different during the weekends when the power consumption is lower than during the weekdays. Such an effect might be possibly present in the European region, but it is very weak. PLHR effects are less often detected in the summer, as the ionospheric absorption increases, and also, the radiation is obscured by lightning generated emissions. This difference is smaller in the U.S. region, in agreement with the monthly variations of the power consumption. The analysis of the measured frequency spectra reveals that although intensity increases at low odd harmonics of base power system frequencies are routinely detected, low even harmonics are generally absent. Finally, we verify the relation of PLHR intensities to the geomagnetically induced currents (GICs) proxy. It is shown that the PLHR intensity is increased at the times of higher GIC proxy values during the night.

Unexpected Very Low Frequency (VLF) Radio Events Recorded by the Ionospheric Satellite DEMETER

DEMETER was a low Earth orbiting microsatellite in operation between July 2004 and December 2010. Its scientific objective was the study of ionospheric perturbations in relation to seismic activity and man-made activities. Its payload was designed to measure electromagnetic waves over a large frequency range as well as ionospheric plasma parameters (electron and ion densities, fluxes of energetic charged particles). This paper will show both expected and unusual events recorded by the satellite when it was in operation. These latter events have been selected from the DEMETER database because they are rare or even have never been observed before, because they have a very high intensity, or because they are related to abnormalities of the experiments under particular plasma conditions. Some events are related to man-made radio waves emitted by VLF ground-based transmitters or power line harmonic radiation. Natural waves, such as atypical quasi-periodic emissions or uncommon whistlers, are also shown.

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.

Analysis on power line harmonic radiation in China space

Analysis on power line harmonic radiation in China space

Statistical analysis of VLF radio emissions triggered by power line harmonic radiation and observed by the low‐altitude satellite DEMETER

AbstractDEMETER was a low‐altitude satellite in operation between 2004 and 2010 in a circular polar orbit. One of its main scientific objectives was to study ionospheric perturbations related to man‐made activity. This paper investigates electromagnetic emissions triggered by Power Line Harmonic Radiation (PLHR), the man‐made waves emitted at harmonics of 50 or 60 Hz. They look like rising tones or hooks with a starting frequency associated to a parent line with the frequency equal to a multiple of 50 or 60 Hz. They occur preferentially during daytime in a frequency band between 1 and 4 kHz. It is shown that these emissions are rather frequent at high latitudes (3 < L <6) above industrialized areas during periods of moderate magnetic activity. Their average intensity is of the order of 10 μV2 m−2 Hz−1. PLHR propagates in the magnetosphere and triggers emissions due to wave‐particle interactions in the equatorial region.

Propagation characteristics of power line harmonic radiation in the ionosphere

Theoretical model and solutions on power line harmonic radiation (PLHR) propagating in the ground, air, and anisotropic homogeneous ionosphere are presented. The theoretical model is verified by the PLHR events observed by the DEMETER satellite. Some propagation characteristics of PLHR based on the model are obtained. This paper is beneficial to quantitatively interpret the formation mechanism of PLHR phenomenon.

Influence of power line harmonic radiation on the VLF wave activity in the upper ionosphere: Is it capable to trigger new emissions?

We analyze the influence of Power Line Harmonic Radiation (PLHR) events on the overall VLF wave activity as observed by the low‐altitude (about 700 km) DEMETER spacecraft. We take advantage of a unique set of 148 PLHR events identified in the Burst mode data, where a waveform of one electric and one magnetic field component is measured. It is shown that the occurrence rate of PLHR events over the industrialized areas is quite large (more than about 8%). However, among all the identified events, we have found only two cases of possibly PLHR‐triggered emissions. There is no evidence that the total power spectral density of electromagnetic waves over industrialized regions and geomagnetically conjugate regions is larger than what would be expected without man‐made influence. Finally, we have analyzed the presence of the weekend effect (i.e., a different behavior during the weekends as compared to the weekdays due to the lower power consumption), demonstrating that no such phenomenon seems to be present in the analyzed data set.

MLR events and associated triggered emissions observed by DEMETER

This paper gives an overview of different sets of new Magnetospheric Line Radiation (MLR) observed by the satellite DEMETER. Different types of emissions have been observed: emissions called Power Line Harmonic Radiation (PLHR) with frequency lines exactly separated by 50/100 or 60/120 Hz, emissions with frequency lines not exactly separated by 50/100 or 60/120 Hz and drifting in frequency (MLR). By comparison with past observations one can say that some MLR events are due to man-made PLHR which may suffer a non-linear gyro-resonant interaction at the magnetic equator. It is also shown that periodic emissions are very often associated with the MLR. In this case the origin of these waves is natural. The lines are produced by the periodicity and the frequency band limits of the individual elements which causes the appearance of lines on the spectrograms. Finally the paper shows that MLR can trigger emissions.

Survey of magnetospheric line radiation events observed by the DEMETER spacecraft

Magnetospheric line radiation (MLR) events are electromagnetic waves in the frequency range between about 1 and 8 kHz that, when presented as a frequency‐time spectrogram, take the form of nearly parallel and clearly defined lines, which sometimes drift slightly in frequency. They have been observed both by satellites and ground‐based instruments, but their origin is still unclear. We present a survey of these MLR waves observed by the DEMETER spacecraft (at an altitude of about 700 km). Three years of VLF Survey mode data were manually searched for MLR events, creating the largest event satellite database of about 650 events, which was then used to investigate the wave properties and geographical occurrence. Finally, the most favorable geomagnetic conditions (Kp and Dst indices) for the occurrence of MLR events have been found. It is shown that MLR events occur mostly at L > 2 (upper limit is given by a limitation of the spacecraft), they occur primarily inside the plasmasphere, and there is a lower number of events occurring over the Atlantic Ocean than elsewhere on the globe. The MLR events occur more often during the day and usually during, or after, periods of higher magnetic activity. Their frequencies usually lay between about 2 and 6 kHz, with the total frequency bandwidth of an observation being below 2 kHz in the majority of cases. Moreover, it is shown that the longitudinal dimensions of the MLR events can be as large as 100° and they can last for up to a few hours. Finally, we discuss a possibility that MLR events may be triggered by power line harmonic radiation (PLHR) and we report an event supporting this hypothesis.