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This article presents an experiment of rocket-triggered lightning to 10 kV power distribution lines and the characteristics of lightning current at Guangzhou Field Experiment Site for Lightning Research and Testing during 2018–2019. The return strokes (RSs) current of the triggered-lightning flashes in this study exhibits a shorter half-peak width and similar risetime and peak current compared with those of subsequent strokes current from natural lightning. The peak current of RSs shows strong power function correlations with charge transfer within 1 ms and action integral within 1 ms of RSs, with R2 of 0.80 and 0.92, respectively. Besides, the peak current of RSs is proportional to the average rate rise of RSs (dI/dt). We recommend the double HEIDLER function to simulate the RS current and provide accurate raw data for the study of lightning protection.

In this article, we analyzed the difference in the estimated currents from the Foshan Total Lightning Location System (FTLLS) under two triggered lightning situations, i.e., triggered lightning to ground and triggered lightning to the distribution line. FTLLS underestimated the peak currents of triggered lightning to the distribution line, which is reflected in the peak far electric field. The peak far electric field of triggered lightning to the distribution line is about 12% lower than that of triggered lightning to ground. However, this difference in estimated current is not reflected in the far electric field waveform parameters, at least for the three field parameters: zero to peak risetime, 10%–90% risetime, and half-peak width time. The presence of distribution line will increase the risetime of the lightning return stroke current, the arithmetic mean of the current risetime of triggered lightning to distribution line is 0.46 μs, and that of triggered lightning to ground is 0.27 μs. Clarification of this underestimation phenomenon is beneficial for the application of the lightning location system in power systems.

In this article, we analyzed the characteristic parameters of close vertical electric field waveforms from triggered lightning at 58 and 90 m obtained at Conghua, Guangzhou, in the summer of 2019. A total of 11 characteristic parameters were defined, including leader electric field peak [kV/m] (E $_L$ ), return stroke electric field change [kV/m] (E $_RS$ ), zero-to-peak rise time [μs] (T $_1$ ), 10-to-90% rise time [μs] (T $_2$ ), half-peak width [μs] (T $_3$ ), zero-crossing time [μs] (T $_4$ ), slow-front duration [μs] (T $_5$ ), opposite polarity overshoot duration [μs] (T $_6$ ), fast-transition 10-to-90% rise time [μs] (T $_7$ ), opposite polarity overshoot ratio [%] (E $_OS$ /E $_L$ ), and slow-front magnitude relative to peak [%] (E $_S$ /E $_L$ ). The arithmetic mean, geometric mean, and standard deviation of each parameter were counted. Data comparison results at 58 and 90 m show that T $_1$ –T $_7$ at 90 m were larger than those at 58 m. E $_L$ and E $_RS$ at 90 m were both positively correlated with the peak current [kA] (I $_P$ ). The influence of distance on this correlation was also analyzed. The half-peak width of the current waveform was inversely proportional to that of the electric field waveform.

The effects of long upward connecting leader (UCL) channel on electromagnetic fields for lightning striking to tall towers are studied via lightning transmission-line return-stroke model. The current distributions along the lightning channel and the tower are derived, and the resultant lightning electromagnetic fields with various UCL lengths above tower are calculated at close and far distances. It can be found that the contribution of the various components of the electric and magnetic fields depends strongly on the distance to the observation point. Electric field has a shading effect showing that the field amplitude generated by lightning striking to tall towers is smaller than that to ground, and that this shading effect depends on the UCL length and the tower height. However, we cannot find such an effect for the magnetic field. The shading effect of the electric field increases with the increase of the junction height above tower, but disappears when the observation distance exceeds a critical distance. Modeled results are also compared with their measured counterparts associated with lightning striking to the 600 m tall Canton Tower. The proposed model can explain why the ratios of peaks of luminosity to magnetic field of the downward first stroke are considerably larger than those of the subsequent strokes as being due to the fact that the junction height above tower for first stroke is higher than that for subsequent stroke, whereas the downward return stroke speed of first stroke is smaller than that of subsequent stroke.

In this article, we present a theoretical evaluation of instrumental decay time on the lightning electric field waveforms excited by lightning M -components. Fast and slow M -component waveforms were adopted as the injected lightning current. Simulation results for the electric field waveforms at 100 m and 15 km are presented. The results show that the M -component electric field waveforms suffer noticeable distortion when the flat antennas are characterized by small analog integrator time constants. The waveform distortions were defined in this article. It is shown that, compared to the electric field waveforms of the fast M -component, the electric fields of the slow M -component suffered larger distortion. This article emphasizes the importance of the taking into account of the instrumental decay time in lightning M -component electric field waveforms.

The authors present a statistical analysis of characteristics of magnetic fields at different distances from triggered lightning experiments on Transmission Line at Guangdong Comprehensive Observation Experiment on Lightning Discharge during the summer of 2019. The histograms and parameters of statistical distributions for the following 22 waveform characteristics are presented, including current peak, 10%–90% risetime, half‐peak width and steepness, leader magnetic field peak, return‐stroke magnetic field peak, magnetic field peak, 10%–90% risetime, half‐peak width and steepness at 15 m, 130 m and 1.55 km. The arithmetic mean of 48 return stroke current peaks is 18.3 kA and the geometric mean is 17.0 kA. The arithmetic and geometric means of the current 10%–90% risetime are 0.6 and 0.6 μs, respectively. The leader magnetic field, return‐stroke magnetic field and magnetic field peak at 18 m, 130 m and 1.55 km are shown linear relationship with current peak values. With increasing the distance(r), the magnetic field peak value decrease, combining the magnetic field characteristics reported by previous studies, the analysis of all magnetic field peaks in different distances suggest linear relationship with r −0.90. The magnetic field 10%–90% risetime shows linear relationship with ln(r) and half‐peak width did not show significant correlation with distance.

This paper presents the induced voltage measured at the terminal of a 10 kV distribution line when triggered lightning taking place at a distance of 40 m. It is shown that the induced voltage waveforms exhibit three components including a slow increase preceding the initial negative peak, following a rapid polarity reversal and the attenuated oscillations. The waveform parameters are defined in this paper. The observed negative peak value ranges from −47.1 kV to −7.5 kV. The positive peak value ranges from 5.3 kV to 20.9 kV, and the peak to peak value ranges from 12.8 kV to 63.2 kV. The test results show that the negative peak value of the induced voltage at the terminal of distribution generated by nearby negative triggered lightning generally exceeds the positive peak value, and in some cases the negative peak value even reaches twice the positive peak value. The negative 10%-90% rise time ranges from 2.3 μs to 88.5 μs, and the average oscillation period is about 18 μs. Both negative and positive peaks of induced voltages show good linear relationship with the peaks of lightning return stroke current.

This paper reveals the characteristics of thunderstorm dynamic movement using total lightning data obtained from the VLF/LF measurement. Eight thunderstorms, which was evenly distributed in the morning, midday, afternoon and evening, are selected to compare the different kinematic features around the Pearl River Delta (PRD) region in the south of China from 17 May to 23 May 2014. The connected-neighborhood labeling method is used to identify lightning clusters and obtain the centroids. Significant characterization parameters are put forward as metrics to reveal the kinematic features of thunderstorms, including the duration, valid area (VA), velocity, direction, and farthest distance in longitude and latitude during the life cycle of storm. A common trend is that the storms initiate in the west of the PRD region, moving to the east and disappearing after the thunderstorm travels around 106.5 km in longitude. There are two kinds of distribution to depict the property of valid area, which are one-peak distribution with the maximum in the mature stage and two-peak distribution with a relatively smaller peak in the early time of storm. The velocity does not show the same trend as the variation of VA which shows the steady increase or decrease during the lifetime of thunderstorm. The biggest VA and highest velocity are 891 km2 occurred on the evening of 17 May and 204.8 km h−1 occurred on the morning of 20 May. The 19 May evening storm was the weakest, with the maximum of VA and velocity being 253 km2 and 115.3 km h−1, respectively. The motion of storms shows a distinct pattern, as the spread of direction distributes tightly in the range of 0°–90° and 270°–360°. The movement characteristics of thunderstorm and the associated parameters may help to improve the nowcasting and forecasting system of thunderstorms in this region.

The radiated electric field produced by lightning plays a vital role in lightning location systems (LLSs). The presence of the elevated objects, i.e. transmission lines in the presented study, result in an increase of amplitude and multiple sub-peaks in the observed electric fields. On the basis of the electric fields obtained from multiple sensors of Foshan total LLS, electric fields from nine negative lightning strokes associated with transmission-line faults at a distance of 10-86 km in Foshan area were examined in detail, which were adopted to make comparison with the radiated electric fields from natural negative cloud-to-ground lightning detected nearby within 1 min. It can be found that the arithmetic means (AMs) of initial electric-field peak values of waveforms associated with transmission-line faults are about twice those of natural negative lightning and the second and third sub-peaks can be identified obviously. In addition, the correlation between electric-field waveform characteristics and propagation distance was validated. The AM zero-crossing time, fast-transition 10-90% rise time and the time interval between sub-peaks slightly increase with distance.

We present a new engineering model for the M component mode of charge transfer to ground that can predict the observed electric field signatures associated with this process at various distances, including (a) the microsecond-scale pulse thought to be due to the junction of in-cloud leaders and the grounded, current-carrying channel and (b) the ensuing slow, millisecond-scale pulse due to the M component proper occurring below the junction point. We examine the features of 13 microsecond-scale, fast electric field pulses associated with M component processes in upward negative lightning initiated from the Santis Tower and recorded 14.7 km from it. Eleven out of the 13 pulses were found to be unipolar with pulse widths in the range of 9.8 to 35 mu s, and the other two were bipolar. To model the process that gives rise to microsecond-scale pulses, we hypothesize that the current pulses propagating away from the junction point along the main lightning channel (below the junction point) and along the feeding in-cloud leader channel (branch) carry the same amount of charge. We further assume that the pulse traversing the branch is similar to a subsequent return-stroke (RS) pulse. In the model, the RS-like process is represented by the MTLE model. The millisecond-scale field signature that follows the initial fast pulse in M components at close distances is simulated in our model using the guided-wave M component model. The proposed model successfully reproduces the vertical electric field waveforms associated with M-component processes in upward lightning flashes initiated from the Santis Tower at 14.7-km distance from the lightning channel, in which both the fast, microsecond-scale and the following slower, millisecond-scale pulses were observed. The model also reasonably reproduces the known features of electric field signatures at close distances (up to 5 km), where the amplitude of the millisecond-scale hook-like pulse is much larger than that of the microsecond-scale pulse, and at far distances (of the order of 100 km), where the microsecond-scale pulses are dominant. Key Points The new engineering M component model can reproduce the microsecond-scale electric field pulses thought to be due to the junction process The proposed model can be used to simulate both the microsecond- and millisecond-scale features of M component field signatures at close and far ranges The geometry of the in-cloud leader channel and the junction point height largely determine the presence of the microsecond-scale electric field pulses

Wind turbines are very vulnerable to lightning strikes due to their height, sharp edges and remote locations often with high soil resistivity. In this paper we present numerical simulations of the impedance of a typical wind turbine grounding geometry. We analyze the influence of interconnecting grounding systems of different wind turbines. IEC TR61400-24 suggests interconnection of grounding electrodes of wind turbines through horizontal electrodes (in the form of insulated or bare conductors) to achieve low steady-state grounding resistance. The analysis takes into account the frequency dependence of the soil electrical parameters. We show that the low frequency grounding impedance can be reduced by a factor of two or more as a result of interconnecting grounding systems. However, the reduction is significantly lower at higher frequencies because of the interconnection wire’s inductance. We analyze the spatial distribution of the ground potential rise and step voltage in response to typical first and subsequent lightning return stroke current waveforms. It is shown that both, ground potential rise and step voltage can be significant along the wire, especially for high resistivity soil, and placing sensitive equipment near the interconnecting wire should be either avoided, or insulated wire should be used.

We present here an engineering return-stroke model for lightning striking to tall towers with taking into account the presence of the upward connecting leader (UCL). The current distributions along the lightning channel and the tower are derived, and the resultant lightning electromagnetic fields with various lengths of UCL above tower are calculated via a transmission line model. Obtained results indicate the electric field has a shading effect showing that the field amplitude generated by lightning striking to tall towers is smaller than that to ground, and that this shading effect depends on the length of UCL. The shading effect of the electric field increases with the increase of the junction height above tower, but disappears when the observation distance exceeds a critical distance. Modeled results are also compared with their measured counterparts associated with lightning striking to the 600-m tall Canton Tower in the literature.

International audience; Simultaneous measurements of current and multiple-station electric fields associated with a 5.4-kA-peak M-component in rocket-triggered lightning are presented in this study. A close-range electric field measurement site was located northeast of the triggering site, 195°clockwise from South, at a distance of 78 m, while the distant multiple stations in this study were located southwest of the lightning triggering site (25-48°, clockwise from South) at a distance ranging from 69 to 126 km. Both the fast microsecond-scale and slow millisecond-scale pulses were observed at six distant stations. At the close station, the fast pulse was not noticeable. The magnitude and half-peak width of the fast pulse were in the range of 0.91-1.93 V/m and 2.0-3.0 μs, respectively. The corresponding parameters for the slow pulse were, respectively, in the range of 0.59-1.29 V/m and 20.0-25.1 μs. The time lag between the onset of the channel-base current and the far electric field of the M-component was 18 μs. This time lag was used to deduce the ratio of the M-component channel length and the wave speed. The classical guided wave M-component model proposed by Rakov et al. (1995, https://doi.org/10.1029/95JD01924) to simulate the slow, millisecond-scale field pulse assumes that neither the incident nor the reflected current wave undergoes attenuation even though the wave propagation occurs along a lossy channel. A modified guided wave M-component model is proposed in this study in which the M-component current wave attenuates with an exponential decay. Based on the best agreement achieved between the simulated fields using the modified two-wave M-component model and the observed near and far electric fields, the channel length, the M-component wave speed, and the current attenuation constant were inferred, respectively, as 1.8 km, 1 × 10 8 m/s, and 3 km. It is shown that the modified guided wave M-component model is able to reproduce reasonably well the electric fields both at close and far distance ranges.

The electric field measurements of lightning-produced electromagnetic fields are of great importance for lightning location system. In 2014, based on the simultaneously obtained electric fields from multiple sensors of Foshan Total Lightning Location System (FTLLS), 27 natural negative cloud-to-ground (CG) lightning flashes containing 168 electric field waveforms at a distance of 10–86 km in Foshan area were examined in detail. The arithmetic mean (AM) value of initial electric field peak normalized to 100 km for 168 field waveforms is 5.1 V/m. The AM zero-to-peak and 10-90% risetime are 5.6μm and 1.4μm, the AM half-peak width and slow-front duration is 2.5μm and 3.7μm, respectively. The AM zero-crossing time and ratio of peak value to opposite polarity overshoot for 142 waveforms are 31.2μm and 10.5%. The AM second sub-peak amplitudes relative to the initial and the time interval between initial and second peaks are 43.3% and 2.5μm, respectively. In addition, the correlation between electric field waveform characteristics and propagation distance was examined. Some degree of distance dependence for several parameters were also observed.

This paper statistically analyzed electric field waveform parameters of 56 negative triggered lightning return strokes at the distance of 58 m obtained at Guangzhou Field Experiment Site for Lightning Research and Testing (GFESLRT) during the summer of 2019. In addition, the correlation between the electric field peak and the current peak at the bottom of the lightning channel has also been analyzed. The statistical results in this paper extend the database of detailed close electric field waveform parameters of triggered lightning leader/return stroke.

Return-stroke current and electric field play important roles in atmospheric electricity research. Aim of this paper is to examine the empirical formulas for calculating return-stroke peak-current in lightning location system according to sensored peak-electric-field, and to evaluate the detection efficiencies and the peak-current estimation of the Foshan Total Lightning Location System (FTLLS). Lightning was initiated artificially by rocket triggering procedure and the current waveform was recorded at the lightning channel-base. A total of 43 return-strokes in 8 flashes were triggered succesfully in 2014. Nine different regression formulas providing the best fit to the measured current-and-field data were derived. The empirical formulas were based on the directly measured return-stroke current and electric fields of 38 return-strokes within 4 flashes. The empirical formulas analyzed in the present study demonstrate the regional difference of the empirical formulas for various geographical-distributed stations of the FTLLS in Foshan, China. On the other hand, the return-stroke speeds were theoretically derived though the transmission line model considering the already known parameters of the corresponding measured-peak-current at triggering lightning site. The nine empirical formulas from the nine stations of the FTLLS were analyzed by the fact that the values of the inferred return-stroke speeds for each return-stroke and for each station are reasonable compared to those in the previous literatures. In addition, the detection efficiencies and peak-current estimation of the FTLLS and the LLS of Guangdong power grid in Guangdong Province were examined and were compared based on the directly measured current data at the triggering lightning site. It is shown that the detection efficiencies of the FTLLS for flashes and for return-strokes were 87.5% (7/8) and 93.0% (40/43), respectively. The peak-current estimation error reported by the FTLLS was 8% on average. The absolute value of the maximum error for the individual return-strokes were around 28%. Performance comparison to other global/regional lightning location systems are also presented.

Far-field measurements of lightning-produced electromagnetic fields are of high importance for lightning location systems. Data from recorded lightning strokes can be, for example, used to assess the risk of lightning-induced damage in some geographical areas. Artificially triggered lightning, usually generated using rocket-wire technology, plays an important role in the study of lightning physics. Multiple-station observations of far (typically larger than 20 km) electric field waveforms produced by rocket- triggered lightning are quite rare. In 2014, electric field waveforms were measured for return strokes through the rocket-and-wire technique at Conghua. They were measured by electric field sensors at nine sites belonging to the lightning locating system in Foshan, Guangzhou, China. A total of 38 events were recorded and overall statistics of those waveforms are presented. The results were compared to previous experimental data related to natural and artificially triggered lightning to validate their similarity.

Wind turbines are very vulnerable to lightning because of their height, sharp edges and remote locations often with low soil conductivity. In this paper we present numerical simulations of the impedance of a typical wind turbine grounding geometry. We analyze the effect of interconnecting grounding systems of different wind turbines. IEC TR61400-24 suggests interconnection of grounding electrodes of wind turbines through horizontal electrodes (in the form of insulated or bare conductors) to achieve low steady-state grounding resistance. The analysis takes into account frequency dependent soil parameters. It is shown that the low frequency grounding impedance is reduced by a factor of two or more. However, the reduction is lower at higher frequencies because of the interconnection wire's inductance.

The purpose of the paper is to investigate charge transfer modes in upward lightning flashes by means of numerical simulation constrained by concurrent observations of electromagnetic fields and currents. In particular, we focus on different types of pulses occurring in upward negative flashes. The MTLE return stroke model is used to compute the electric fields associated with return strokes and mixed-mode pulses, while the M-component model of Rakov et al. (1995) is used to compute electric fields associated with M-components and M-component-type ICC pulses. The simulation results are constrained by experimental data consisting of simultaneous records of lightning currents and electric fields associated with upward flashes at the Santis tower. The inferred velocities for M-component and M-component-type ICC pulses range from 2.0x10(7) m/s to 9.0x10(7) m/s, and the corresponding junction point heights range from 1.0 km to 2.0 km. The inferred pulse velocities for return strokes and mixed-mode pulses range from 1.3x10(8) m/s to 1.65x10(8) m/s. The inferred current attenuation constants of the MTLE model obtained in this study range from 0.3 km to 0.8 km, lower than the value of 2.0 km suggested in previous studies. The obtained results confirm the similarity of mixed-mode charge transfer to ground with return strokes on the one hand, and of the M-component-type ICC with classical M-components mode of charge transfer on the other hand.