Subsequent Return Strokes Research Articles

Attachment processes of negative flashes with multiple return strokes to a tall tower observed at close distances

Two downward negative flashes (F1612 & F1613) with multiple return strokes struck to the 356-m Shenzhen Tower were analyzed. The high-speed camera captured upward positive connecting leaders (UCL) for the first strokes of both flashes and two subsequent strokes of F1612. The observations also show that none of the downward negative leader (DNL) completely propagated to the tower tip before the occurrence of the return stroke (RS), so that we inferred that the UCL initiated from the tower tip might exist for each RS of the two flashes. The possible height of the UCL and DNL connecting point above the tower tip for each RS was estimated, which showed a positive correlation to the speed of corresponding DNL. The striking distances estimated for 8 subsequent RSs in F1612 were in a range from 14.6 m to 85.4 m and that for 3 subsequent RSs in F1613 were from 24.2 m to 66.2 m. There was a weak positive linear relationship between the DNL speed and striking distance for subsequent RSs in the two flashes. The DNL speed showed a positive correlation to the peak current of corresponding RS.

A simplified time domain approach to calculate lightning electric fields considering the grounded tower-line-tower (TLT) structure

This study describes a method for calculating electric fields radiated by lightning in the presence of a tower-line-tower (TLT) structure, extending a previous method developed by Rachidi et al. (2002). The method involves using a lattice diagram to analyze current distribution and deriving expressions related to the current distribution along the lightning channel and the TLT structure. Expressions associated with the current distribution along the lightning channel and the TLT structure are derived. The impedances of the towers, the connected overhead grounded wire, and lightning channel were treated as constant values. The subsequent return stroke was analyzed in the paper. The lightning radiated electric fields at an intermediate distance of 15 km considering lightning striking to ground, one single object, and the TLT structure were presented and compared. The directly strike of lightning on a tower plays an important role in the increase of the electric field magnitude, while the neighbored tower and the associated grounded wire contributes to periodical superimpositions on the middle-and-late response of the electric fields. Detail discussion on the influences of the different parameters of the proposed method on the electric fields at 15 km and comparison to the measured data were also presented.

Temporal characteristics of positive cloud-to-ground flashes from tropical thunderstorms

The occurrence of positive cloud-to-ground (CG) lightning flashes proves to be a challenging task when compared to the negative CG flash which common happen in tropical region. This due to the positively charged clouds to reach higher altitudes to enable the transfer of electrical charges to the Earth's surface. With several sensors that deployed in the Malacca region (2.314077°N, 102.318282°E) such as the wide band fast and slow antenna, magnetic field sensors, and the electric field mill (EFM-100). This research study focuses on the temporal characteristics of positive CG lightning activity in the tropical region during September and October 2021. A total of 203 positive cloud-to-ground flashes were meticulously analyzed in the context of 16 thunderstorm events. Key findings highlight the consistent initiation of positive cloud-to-ground flashes through initial breakdown (IB) pulses, followed by the development of stepped leaders and subsequent return strokes. Notably, most positive cloud-to-ground events (72%) were observed as single strokes and the maximum multiplicity recorded being four subsequent return strokes. Furthermore, the analysis focuses into the temporal aspects of these lightning events, revealing average durations for various parameters, including rise-time (6.26 μs), zero-crossing (26.43 μs), pulse duration of the first RS (139.76 μs), and the interval from the first IB to the first return stroke (134.19 ms). Additionally, the recorded data from the Electric Field Mill (EFM) instruments together with Constant Altitude Plan Position Indicator (CAPPI) radar demonstrate a notable correlation. Specifically, the electric field (E-field) values exhibit a discernible increase when positive cloud-to-ground lightning events are detected near the lightning sensor.

Comparison of Lightning Channel Luminosity Versus Time Profiles in the Infrared and Visible Ranges

AbstractInfrared (IR) luminosity of lightning channel in the 3–5 μm range usually persisted throughout the entire interstroke interval, which is in contrast to the simultaneously recorded visible (0.4–0.8 μm) luminosity that always decayed to an undetectable level prior to a subsequent return stroke pulse. A longer visible luminosity period at the end of flash tended to be associated with a longer IR afterglow period following the decay of visible luminosity (and by inference current) to an undetectable level. At the end of flash, the IR luminosity persisted up to about 1 s, and the median IR afterglow duration was a factor of 10 longer than the median visible luminosity duration. The IR luminosity often exhibited a hump when the visible luminosity was monotonically decaying or undetectable, with the corresponding channel temperature being likely around 3400 K.

Electromagnetic fields of lightning return stroke to wind turbines with discontinuous impedance model

This study introduces an electric field calculation model for wind turbine return strokes, incorporating impedance discontinuity within the turbine, a feature not considered in traditional tall tower models. The model introduces a reflection coefficient, ρx, at the connection between the blades and the tower. Disregarding the generation of upward leaders, this paper calculates the electric field of subsequent return strokes for different distances from the wind turbine and for different model parameters. The results demonstrate that changes in the reflection coefficient ρx affect oscillation amplitude and also slightly influence the pulse width, with a negative ρx leading to smaller and more frequent pulses. Contrasts with measured waveforms indicate that models with a constant reflection coefficient are inaccurate. Adopting variable reflection coefficient values yields a more accurate match. This approach offers a new perspective for electromagnetic field calculations in lightning-struck structures, emphasizing the significance of impedance dynamics of return stroke channel.

FDTD-based computational model applied to assess the influence of the frequency dependence of soil parameters on the lightning response of grounding electrodes for typical parameters of first and subsequent return stroke currents

This paper considers an evaluation of the influence of the frequency-dependence of soil parameters on the lightning response of horizontal grounding electrodes by means of the finite-difference time domain (FDTD) electromagnetic model. The FDTD simulations assumed the soil modeled as a multipole Debye medium and the response of grounding electrodes due to lightning return stroke currents with typical front time parameters of negative first and subsequent strokes was assessed. The results in terms of the ground potential rise (GPR) and grounding impulse impedance (ZP), were compared to those provided by the application of the Hybrid Electromagnetic Model (HEM), a frequency domain model widely applied for lightning related problems, and revealed the top quality of the modeled approach in FDTD. The largest percentage variations of the calculated impulse impedance compared to HEM were around 6 % and 10 % for first and subsequent stroke currents, respectively.

Parameters of the Initial Continuous Current of Negative Upward Lightning Measured at the Peissenberg Tower, Germany, From 1992 to 2022

In this article, we analyze the parameters of the initial continuous current (ICC) of the negative upward lightning measured at the Peissenberg Tower, Germany, from 1992 to 2022. A total of 54.9% of them were ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Only</sub> -flashes (without significant ICC-pulse), 24.0% of them were ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RS</sub> -flashes (with subsequent return stroke), 19.6% of them were ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> -flashes (with ICC-pulses > 2 kA), and 1.5% of them were ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bipolar</sub> -flashes (succeeded by a positive current component). The analysis revealed that the ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Only</sub> -flashes were the weakest ones, the ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> -flashes were the strongest ones, and the ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RS</sub> -flashes and the rare ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bipolar</sub> -flashes were in between. Out of the total of 204 measured ICCs, 16 (7.8%) of them exceeded the charge of 200 C, which represents the highest tolerable level according to the lightning protection standard IEC 62305-1. The strong ICC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> -flashes carried charges up to 454 C, being more than twice of this tolerable level.

Differences Between Far Electric Field Waveforms of Triggered Return Strokes and Natural Return Strokes From Nine Thunderstorms

The far electric field waveforms of natural first return strokes (FRSs), natural subsequent return strokes (SRSs), and triggered return strokes (TRSs) from nine thunderstorms measured by the same device were compared. The results were as follows: The far electric field peaks of TRSs were 31% smaller than that of SRSs. The geometric means of 10-to-90% risetime and half-peak width of SRS far electric fields are 2.4 μs and 5.4 μs, respectively, while those of TRSs are significantly smaller, i.e., 1.5 μs and 3.2 μs, respectively. Three possible reasons cause the differences between the SRS and TRS far electric field waveforms: TRS and SRS occur in different cloud conditions; triggering experiments are more likely to be successful when the thunderstorm electric field is in a stable period; the rise of the TRS current is steeper. Two possible reasons cause the steeper rise in TRS current: the lower part of the TRS channel is more conductive; the lower part of the TRS channel is shorter than that of the SRS channel.

Transient analysis of power transmission towers above lossy ground with frequency dependent electrical parameters considering the water content of soil

Adequate soil modeling is fundamental to assessing the grounding impedance of the grounding system and the transient responses in power systems. This paper aims to investigate three soil models with electrical parameters varying with frequency and water content, namely Smith-Longmire, Scott, and Messier models, and their impact on the ground potential rise (GPR) waveforms of vertical grounding rods. Besides that, the transient induced voltages across the string of insulators induced are also investigated for lightning currents representative first, and subsequent return strokes are employed. The harmonic grounding impedance (HGI) is calculated for rods of 3, 15, and 30 m buried in frequency-dependent (FD) soil model using commercial electromagnetic software (FEKO) with the Method of Moments (MoM) for a range of 100 Hz to 10 MHz. Simulation results show a significant modification of the calculated HGI beyond a particular frequency. The induced transient GPR waveforms show a notable reduction in their voltage peaks when the FD soil model is compared with those computed using the frequency-independent (FI) soil model. Finally, a backflashover analysis is carried out that demonstrates its dependence on the rod length, water content, and the specific soil model employed.

Alternative study to reduce backflashovers using tower-footing grounding systems with multiple inclined rods

This paper investigates the influence of the inclination angle on the harmonic grounding impedance (HGI) of three arrangements with multiple rods. Then, Ground Potential Rise (GPR) and the lightning performance (backflashover prediction) on transmission towers using these grounding systems are studied. A full-wave electromagnetic software FEKO using Method of Moments (MoM) is utilized to compute the HGI in a frequency range of 100 Hz to 10 MHz, assuming the soil with low-frequency resistivity of 1,000 Ω m and modeled considering the frequency effect on the ground parameters. The analysis is carried out for grounding systems of multiple rods composed of 2, 3, and 4 inclined electrodes considering inclination angles of 0°, 15°, 30°, 45° and 60°. The transient GPR developed for the first and subsequent return strokes are evaluated. The calculated HGI showed expressive differences for each topology and also for various inclination angles. Consequently, transient GPR waveforms present expressive mitigation for each grounding system whose difference can be obtained only by varying the inclination angle of the rods. Finally, the backflashover probability is reduced when these arrangements with multiple rods combined with highly inclined electrodes are used as tower-footing grounding systems, improving the lightning performance of power systems. • Harmonic impedance of inclined rods is computed for frequency-dependent soil. • GPR is significantly influenced for arrangements with multiple electrodes and angle. • Backflashover is reduced when multiple rods are used as a grounding system. • These arrangements are an alternative for lines located in limited urban areas.

On the processes leading to different modes of charge transfer in negative flashes according to fast videos and correlated records of current and electric field

This work discusses the processes involved in different modes of charge transfer in negative lightning flashes, taking as reference video-records obtained with a fast camera and records of current and close electric-field measured at Morro do Cachimbo Station. The data of two downward and one upward negative flashes are explored for considering the features of these processes and for supporting their interpretation, based on the bidirectional and bipolar leader approach. The processes comprise three sequences (stepped leader - first return stroke, dart leader - subsequent return stroke, dart-stepped leader - subsequent return stroke), in addition to the initial continuous current in upward lightning, return strokes following it, continuing current and M-components, the latter observed superimposed on both the continuing current and the tail of return stroke currents. An unreported process of charge transfer, consisting of the reignition of the dissipating leader of an upward lightning from the ground to the cloud is analyzed as well.

Differences of Electric Field Parameters for Lightning Strikes on Tall Towers and Nonelevated Objects

In this article, we analyzed the far electric field parameters of cloud-to-ground (CG) lightning striking tall towers in Guangzhou at the distance of 20–70 km, and compared with lightning striking nonelevated objects from the same thunderstorm near the tall towers. By comparing the waveform characteristics, we found that the far-field waveform of tall tower exhibits the characteristics of early narrow undershoot, zero crossing, oscillation damping attenuation and there is a secondary peak after the opposite polarity peak, which is absent in the CG lightning. The GM values of 10%–90% rise time, fall time and zero-crossing time of lightning strikes on tall towers are 1.6, 2.0, and 8.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s which are far less than 2.5 (1.8 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s), 7.9 (6.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s), and 28.1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s (28.7 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s) of the first return stroke (subsequent return stroke) of CG lightning. In addition, the initial electric field peak, the ratio of the opposite polarity overshoot amplitude to the initial peak, and the time interval between initial electric field peak and second peak of the lightning striking on tall tower are larger than those of the CG lightning.

Modeling soil ionization effect based on experimental data

• Measurements of Soil Ionization. • Modeling Soil Ionization effect based on experimental data. • Means for estimating soil ionization on the response of grounding electrodes. • Ionization of soils subjected to uniform electric field. • Ionization of soils subjected to non-uniform radial electric field. Results of a huge number of experimental tests involving soil ionization developed by the authors were used in this paper for analyzing the phenomenon and developing means for predicting the effect on the response of grounding electrodes subjected to lightning currents. These results refer to samples of fifteen different soils (from about 100 to 10,000 Ωm at natural moist content) subjected to impulsive current waves exhibiting front times similar to those of first and subsequent return stroke currents. The tests considered conditions of uniform and radial non-uniform electric fields with intensities comparable to those resulting from the impression of real lightning currents on grounding electrodes. A curve was suggested for taking the effect of ionization on the lightning response of electrodes into account for soils in general, by means of an equivalent increase of the electrode radius as a function of the linear density of current dispersed to the soil.

Temporal analysis on pulse train of lightning discharge observed in Malacca, Malaysia

A few significant studies discovered that a pulse train tends to initiate subsequent return stroke in the same way that a preliminary breakdown pulse activates the first return stroke. This paper presents pulse train characteristics in the lightning waveform obtained in Malacca, Malaysia. This study employed 930 pulse train samples divided into twelve groups. Most of the trains are Type IX, i.e., the chaotic pulse train superimposed on the dart leader, accounting for 38% of the samples. There are only 0.8% of Type VI observed in this study. These fewest trains are with regular pulses preceding chaotic pulses without being separated in time. The majority of the pulse train occurred between the first return stroke and the first subsequent return stroke, i.e., 39% of the samples. Averagely, the pulse train time duration was 653μs, and the separation time between pulse train and subsequent return stroke was 25 ms. There was a 99.8% chance that a pulse train would initiate subsequent return stroke. This study revealed that the pulse train and subsequent return stroke separation mean value was decreasing with stroke order. This pattern of pulse train occurrences in the lightning waveform can be manipulated in the lightning monitoring system.

Upward Bipolar Lightning Flashes Originated From the Connection of Recoil Leaders With Intracloud Lightning

AbstractThe present work shows high‐speed videos of two upward flashes that started with positive upward leaders and, instead of being followed by negative subsequent return strokes, they were followed by positive subsequent return strokes. In both cases, after the positive leaders developed, recoil leaders (RL) appeared in their decayed branches as would be usual in negative upward lightning flashes. However, in these flashes the negative end of a recoil leader connected to a positive leader of an intracloud (IC) flash nearby. The connection initiated a downward positive leader that re‐ionized the decayed channel of the upward flash all the way to the tower giving origin to a positive subsequent return stroke. This work shows that RL do play an important role in the occurrence of bipolar upward flashes and their interaction with IC flashes can provide explanations for all types of bipolar upward flashes initiated by upward positive leaders.

Do Wind Turbines Amplify the Effects of Lightning Strikes? A Full-Maxwell Modelling Approach

Wind turbines (WTs) can beseriously damaged by lightning strikes and they can be struck by a significant number of flashes. This should be taken into account when the WT lightning protection system is designed. Moreover, WTs represent a path for the lightning current that can modify the well-known effects of the lightning discharge in terms of radiated electromagnetic fields, which are a source of damage and interference for nearby structures and systems. In this paper, a WT struck by a lightning discharge is analyzed with a full-wave modelling approach, taking into account the details of the WT and its interactions with the lightning channel. The effects of first and subsequent return strokes are analyzed as well as that of the rotation angle of the struck blade. Results show that the lightning current along the WT is mainly affected by the ground reflection and by the reflection between the struck blade and the channel. The computed electromagnetic fields show that, for subsequent return strokes, the presence of a WT almost doubles their magnitude with respect to a lightning striking the ground. Such enhancement is emphasized when the inclined struck blade is considered.

On the Return Stroke Initiated From the Attachment Point Considering Current Reflection From the Ground

In this article, we present an analysis of electric fields and derivative waveforms radiated from lightning return stroke in the presence of an attachment point above the ground. Return stroke initiated from the ground (RSG), return stroke initiated from an attachment point above the ground (RSAP), and return stroke initiated from the attachment point considering current reflection from the ground (RSAPR) were considered and compared. Both first and subsequent return strokes were included in the simulation. It is shown that the presence of the attachment point results in a noticeable initial sharp peak on the electric fields and the derivative waveform was characterized by larger positive peak and negative overshoot. Both the electric field and derivative waveforms in RSAPR were much similar and closer to the results from RSG due to the current reflection from the ground. The influences on the electric fields and derivative waveforms were also discussed, including velocity of upward and downward wave, the attachment point height, reflection coefficient from the ground, and wave velocity of the reflected wave. The simulated results were also compared to the measured fields.

Computation of Lightning-Induced Voltages Considering Ground Impedance of Multi-Conductor Line for Lossy Dispersive Soil

Soil conductivity and permittivity have a substantial influence on lightning-electromagnetic transients in power system. In this paper, lightning-induced voltages are computed on a multi-conductor overhead line due to nearby first and subsequent return strokes. Besides, this study considers the longitudinal complex inductance of the line due to the penetration depth of electromagnetic fields through finitely conducting ground as well as the frequency dependent soil parameters using the finite-difference time-domain method. Various case studies in light of variations of return stroke velocity, line height, and soil conductivity are explored for thoughtful investigations. The obtained results reveal that the influence of this complex inductance on peak values of lightning induced voltages changes with varying the return stroke velocity. Also, the frequency dependence of soil parameters markedly impacts the computed lightning-induced voltages particularly for poor soil conductivity.

Electric fields calculation of lightning return-strokes in the presence of an attachment point above the ground

The radiated electromagnetic fields and derivative waveforms from lightning discharge were directly related with its inner physical process. The return stroke initiated from ground (RSG) and the return stroke initiated from an attachment point (RSAP) were analyzed. Two types of current waveform from Gamerota et al. (2012) and Rachidi et al. (2001), including both the first and subsequent return strokes, were simulated in the presented paper. Both waveforms of the electric field and electric field derivative were analyzed. The electric fields were characterized by an obvious superimposed initial peak on the rising edge, the electric field derivative was featured by a bipolar waveshape with noticeably negative overshoot in the second cycle. The downward return stroke current component is the main reason for the superimposed initial peak in the electric field and the bipolar waveshape with noticeably negative overshoot in the electric field derivative. The subsequent return stroke with larger max steepness from Gamerota et al. (2012) shows more noticeable superimposed initial peak than that of Rachidi et al. (2001). The subsequent return stroke shows more noticeable differences than that of the first return stroke. The peak value enhancements at 100 km are similar to that at 15 km. The changes were less than 0.5% for first return strokes, and 1.5% for subsequent return strokes. Parameter sensitivity on the electric fields and derivative waveforms were also presented.

Electrical Field Parameters of Natural Return Strokes at Different Distances

This article presents the electric field waveforms of natural return strokes recorded by Foshan Total Lightning Location System. The distance ranges from 10 to 300 km. The evolution of parameters for positive first and negative first and subsequent return stroke electric field waveforms along with distance change is analyzed. The results show that the risetime, fall time, half-peak width, and zero-crossing time become longer with longer distance, and these four parameters of the negative return strokes show more clear linear relation with distance than the positive return strokes. For the overshoot duration, the values for both positive and negative return strokes increase with distance at 10–200 km, but when the distance is larger, the distance dependence becomes less obvious. The values of the initial peak normalized to 100 km and 20 kA remain the same in general for all the return strokes. For the overshoot amplitude and the ratio of overshoot to initial peak, the values for both positive and negative return strokes increase with distance. The return stroke electric field waveforms at far distances are more likely to show clear opposite polarity overshoot.