Stroke Current Research Articles

Electromagnetic Fields Radiated by Lightning Return Stroke Over Lossy Ground With Rock Formation

Electromagnetic fields radiated by a lightning return stroke over lossy ground are calculated by finite difference time domain method in a two-dimensional cylindrical coordinate system. The considered ground model contains a rock formation for which four different geometries are defined: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rectangle</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">triangle</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">circle,</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">random</i> . Two electrical conductivities that are very low and very high compared to the conductivity of the ground are defined for the rock formation. Different scenarios are examined by computing horizontal electric field <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{E}}_{\boldsymbol{r}}}$</tex-math></inline-formula> , vertical electric field <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{E}}_{\boldsymbol{z}}}$</tex-math></inline-formula> , and azimuthal magnetic field <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{H}}_{\boldsymbol{\varphi }}}$</tex-math></inline-formula> for both conductivities. In addition to the effect of different geometries, effects of spatial averaging, changing position of rock, different return stroke propagation speeds, observation points at different heights and different horizontal range distances are investigated adopting both first and subsequent return stroke currents as the source. The results show that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{E}}_{\boldsymbol{z}}}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{H}}_{\boldsymbol{\varphi }}}$</tex-math></inline-formula> fields are not much affected by geometry and conductivity change. However, for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{E}}_{\boldsymbol{r}}}$</tex-math></inline-formula> component, performances of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rectangle</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">triangle</i> geometries are close to each other and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">random</i> one shows closest performance to that of the case when there is no rock inside the ground. On the other hand, the field values decrease as the rock conductivity increases for both stroke types.

Observation of Terrestrial Gamma‐Ray Flashes at Mid Latitude

AbstractWe present a sample of Terrestrial Gamma‐ray Flashes (TGFs) observed at mid latitudes by the Atmosphere Space Interaction Monitor (ASIM). The events were detected between June 2018 and August 2020 in the latitude bands between 35° and 51° in both hemispheres, which we hereafter refer to as “mid latitudes.” The sample includes the first observations above and consists of 14 events clustered in four geographical regions: north‐west Atlantic and eastern USA; Mediterranean Sea; the ocean around South Africa; and north‐eastern China and Siberia. We examine the characteristics of each event, both standalone and in the context of the global ASIM TGF data set, and we find that our sample is consistent with the global population concerning the number of counts, but shows significantly shorter durations. We analyze the meteorological context and the general evolution of the parent storms and we show that the storms are not extreme in terms of total duration and extension. Whenever possible, we also include the radio sferics and the peak current of the parent stroke. Finally, we present an estimation of the TGF occurrence rate at mid latitudes, based on ASIM's exposure, the local flash rate and tropopause altitude, and we show that it is outside but very close to two standard deviation from the rate of production at tropical latitudes, corrected by the higher atmospheric absorption of higher latitudes. This means that atmospheric absorption plays a major role in the detection of TGFs at mid latitudes, but we cannot rule out other factors.

Differences Between Flashes With and Without Return Strokes in Rocket‐Triggered Lightning

AbstractBased on simultaneous observation of currents and electric field changes, the differences have been identified between flashes with and without return strokes in rocket‐triggered lightning. The triggered lightning events without return stroke have an obvious no‐current period up to some milliseconds before the current flow is reestablished, then a relatively large amplitude (1.2 kA or so) and fast risetime (0.7 μs or less) pulse similar to those of the return stroke current are reestablished between the upward positive leader and the ground. The triggered lightning events with return strokes have no no‐current period in the initial current variation, and the current pulse of wire destruction and plasma channel reestablishment process is similar to the M‐component pulse, featuring a small amplitude (0.17 kA or so) and slow risetime (57 μs or more). The stronger initial stage is usually followed by return strokes.

Evaluation of lightning location using measured induced voltage obtained from distribution power networks

Lightning location is a significant issue in the protection of transmission lines, renewable energy sources, and electrical equipment. In this article, a new technique for the determination of lightning striking points is been proposed. This method is depending on measured values of lightning-induced voltage obtained from distribution power lines in the vicinity of the lightning channel. The proposed method considers lightning location as well as lightning current wave shape at the channel base. It was validated using a number of measured return stroke currents, and the outcomes are debated accordingly. All electromagnetic field components were taken into consideration in the proposed method, and lightning current wave shape was determined in contrast with the other, widely used methods. Evaluated lightning current wave shapes, based on local measured data, can be used to examine and improve existing protection schemes in renewable energy generation farms, transmission lines, and other power sites. Moreover, lightning maps and ground flash density can be obtained from the evaluated lighting location data to be used in lightning risk assessment studies.

Modeling of Return-Stroke Current Evolution Over a Realistic Ground

The return-stroke phase of the cloud-to-ground lightning flash is of primary concern for lightning-protection engineering. This also holds for buried cables and other sensitive devices in the soil. For evaluating the field in the soil, two approaches are employed: first, the quasi-static approach, in which a current source injects the stroke current into the soil; and second, a hybrid approach employing the “engineering model” for the channel-current evolution. In both the approches, the current injected into the soil is independent of the soil resistivity, which needs further scrutiny. The return-stroke model developed by Balaram Raysaha et al. (2011) self-consistently emulates the stroke-current evolution without any such assumptions and is, therefore, very suitable for a comprehensive assessment of the situation. However, the field-computation method employed by Balaram Raysaha et al. had to be changed to the domain-based finite-difference time-domain method for a realistic soil model. After this augmentation, the return-stroke model is employed to investigate the possible role of soil's electrical parameters on the return-stroke current evolution. It is found that for fast-rising currents of low amplitudes, the soil resistivity noticeably influences the current amplitude. Also, it is found that the soil dispersion leads to a significantly lower electric field in the soil.

Field Enhancement by Lightning Strikes to Tall Tower Versus Lightning Strikes to Flat Ground

When a lightning strikes a high object, the current flows along the object and produces in this way a field component additional to the field radiated from the lightning channel. This additional field component enhances the field compared to lightning to flat ground. In this article, the field enhancement is analyzed for lightning striking the Peissenberg Tower, Germany. The analysis is based on investigations of the far field at distances from 10 to 1000 km. In the computer simulations, the return stroke process is taken into account with the transmission line (TL)-model and the tower is modelled with the computer program CONCEPT II based on the method of moments. In a first step, the pure effect of the tower is analyzed. In this case, the ground is taken into account as perfectly conducting plane. In the next step, the effect of the field propagation is added by introducing an attenuation function based on the solution of Sommerfeld and a far-field approximation of Norton. For fast rising return stroke currents and relatively near distances between 10 and 30 km, the field enhancement may exceed 100%. The field enhancement decreases strongly with decreasing soil conductivity (σ) and increasing distance (s), while the influence of the permittivity (ε) is rather small. At a distance of more than 100 km the field enhancement is typically in the range of some tens of percent. This result agrees well with the data of the European lightning location system EUCLID. From EUCLID an average field enhancement of about 20% is reported for lightning striking the Peissenberg Tower.

Converging Luminosity in Column‐Sprite Filaments

AbstractSprites are electrical discharges in the mesosphere powered by the quasi‐electrostatic field following a cloud‐to‐ground lightning stroke. They are luminous structures with tendrils formed by a space charge wave with high electric fields that ionizes the atmosphere, excites optical emissions and leaves a trail of enhanced densities of electrons, and negative and positive ions. The duration of the luminous streamers in sprites is usually ∼1–10 ms. In this study, we present observations of sprite streamer filaments where the upper and lower ends continue to glow for more than 80 ms while the two ends slowly converge and fade. Simultaneous magnetic observations suggest that the field in the mesosphere is maintained at a high value by the long‐lasting continuing current of the causative stroke. We propose that the observation is a signature of currents in the filaments fed by electrons detached from negative ions at the lower origin.

Winter Positive Cloud‐to‐Ground Lightning Flashes Observed by LMA in Japan

Using a lightning mapping array (LMA), we have observed 24 positive cloud‐to‐ground (CG) flashes occurred in three thunderstorm days. These flashes can be apparently grouped into 5 clusters according to their occurrence times. We have obtained the charge structures for both the individual flashes and clusters. It was found that 4 out of 5 clusters of positive CG flashes exhibited either inverter dipolar or tri‐polar charge structures. This result indicates that the high percentage of positive CG flashes in Hokuriku winter thunderstorms originated from the inverted charge structure rather than the various deformations of normal charge structures widely accepted in literatures. The flash positive charge appeared to distribute usually in a layer with its thickness of around 1 km, its horizontal area of more than 100 km2 and its bottom altitude of around 1–2 km above the ground. For each of the flash, we have also obtained its duration, length, duration before the first stroke and convex area. It was found that all flashes with a large peak return stroke current had short durations before their first return strokes. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Statistical Characteristics of Current and Magnetic Fields at Close Distances From Triggered Lightning

The statistical characteristics of current and magnetic field waveforms from triggered lightning experiments at the Guangzhou Field Experiment Site for Lightning Research and Testing (GFESLRT) during the summer of 2019 are presented in this article. The parameters of statistical distributions of return stroke current are analyzed for peak current, 10–90% risetime, half-peak width, and interstroke interval. The geometric mean of peak current is 12.4 kA. The time-related parameters of the magnetic field at different distances are reported and compared to previous reports of close distances, which indicate the magnetic field 10–90% risetime and 30–90% risetime increase with the distance. The geometric means of the magnetic field peak at 58, 90, and 1600 m are 121.1, 66.2, and 1.85 μT, respectively. The magnetic field shows a positive linear relationship with current peak values. The analysis of all magnetic field peaks at different distances suggests a distance dependence of r −0.92.

The Energy, Momentum, and Peak Power Radiated by Negative Lightning Return Strokes

Electromagnetic radiation fields generated by return strokes transport both energy and momentum from the return stroke to outer space. The momentum transported by the radiation field has only a vertical or z component due to azimuthal symmetry (cylindrical symmetry) associated with a vertical return stroke. In this paper, the energy, momentum, and peak power radiated by return strokes as a function of the return stroke current, return stroke speed, and the zero-crossing time of the radiation fields are studied. The results obtained by numerical simulations for the energy, vertical momentum, and the peak power radiated by lightning return strokes (all parameters normalized by dividing them by the square of the radiation field peak at 100 km) are the following: A typical first return stroke generating a radiation field having a 50 μs zero-crossing time will dissipate field normalized energy of about (1.7–2.5) × 103 J/(V/m)2 and field-normalized vertical momentum of approximately (2.3–3.1) × 10−6 Kg m/s/(V/m)2. A radiation field with a zero-crossing time of 70 μs will dissipate about (2.6–3.4) × 103 J/(V/m)2 in field-normalized energy and (3.2–4.3) × 10−6 Kg m/s/(V/m)2 in field-normalized vertical momentum. The results show that, for a given peak radiation field, the radiated energy and momentum increase with increasing zero-crossing time of the radiation field. The normalized peak power generated by a first return stroke radiation field is about 1.2 × 108 W/(V/m)2 and the peak power is generated within about 5–6 μs from the beginning of the return stroke. Conversely, a typical subsequent return stroke generating a radiation field having a 40 μs zero-crossing time will dissipate field-normalized energy of about (6–9) × 102 J/(V/m)2 and field-normalized vertical momentum of approximately (7.5–11) × 10−7 Kg m/s/(V/m)2. The field-normalized peak power generated by a subsequent return stroke radiation field is about 1.26 × 108 W/(V/m)2 and the peak power is generated within about 0.7–0.8 μs from the beginning of the return stroke. In addition to these parameters, the possible upper bounds for the energy and momentum radiated by return strokes are also presented.

Study on lightning protection scheme of multi‐terminal MMC‐MVDC distribution system

Based on a ±10 kV three-terminal MMC-MVDC (medium voltage DC distribution system based on modular multilevel converter) system, in this study, the authors mainly study on the influencing factors and protection schemes of the lightning intruding overvoltage (including direct lightning and back-flashover lightning). Firstly, a lightning intruding overvoltage simulation model of the MMC-MVDC distribution system using overhead lines is established based on the PSCAD/EMTDC program. The influence of steady-state operating voltage and the number of converter stations on the simulation results are simulated and analysed. Meanwhile, the proper simulation modelling method of the lightning intruding overvoltage for multi-terminal MMC-MVDC system is proposed. Secondly, the lightning intruding overvoltage is simulated when the line is struck by the lightning stroke current that occurs once in 20 years and the different lightning protection schemes are proposed. Finally, based on the lightning impulse withstand voltage, lightning trip-out rate and the cost of the protection schemes, the lightning protection schemes in different scenarios are proposed. The simulation results show that if the cost of the system is prioritised, the protection scheme of increasing the number of parallel stacks of the DL arresters can be selected, and if the power supply reliability of the system is prioritised, the protection scheme of installing the overhead ground wire as well as reducing grounding resistance can be selected.

Observations of single-stroke flashes from five isolated small thunderstorms in East China

This paper presents the ground truth datasets of negative cloud-to-ground (NCG) flashes with one single stroke in five isolated small thunderstorms. By developing a machine-learning method based on the convolutional neural network, we identify the return strokes during the whole life of thunderstorms with the wideband electric field waveform of lightning discharges detected by Jianghuai Area Sferic Array. The distribution of flash multiplicity in these thunderstorms exhibits an exponential decrease pattern. The single-stroke flashes (with multiplicity = 1) account for more than 30% of all NCG flashes on a thunderstorm basis, and the proportion of single-stroke flashes tended to be most abundant. When observed at a 20-min interval, the percentage of single-stroke flashes tends to change dramatically during thunderstorm developments, which seems to show an opposite trend with time to the maximum flash multiplicity. Single-stroke flashes tended to be associated with a weaker peak current of initial stroke compared to that of multiple-stroke flashes. It is inferred that the horizontal scale of negative charge regions in thunderclouds might play an important role in enhancing the flash multiplicity.

Observation of Induced Voltage at the Terminal of 10 kV Distribution Line by Nearby Triggered Lightning

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.

Statistical modeling of lightning propagation in the direction of ground objects

An overview of physical and mathematical modeling methods of lightning leader propagation process in order to compare the effectiveness of their application in the selection of ground object lightning protection is proposed: the study of physical processes using a trigger lightning, launched by a rocket, modeling using electro-geometric methods and fractal models. Detailed statistical modeling that describes the process of moving the lightning leader in the last phase toward the grounded object is considered in detail. The stochastic nature of the leader propagation in the previous stage was used. Using statistical modeling, it is possible to calculate the time of the downward lightning leader propagation from the height at which the leader is oriented to the object, taking into account the possibility of the opposite polarity upward leader emerging from the grounded object. The calculated time of the leader channel propagation from each point in the thunderstorm cloud was used to calculate the probability of attaching a downward leader to a grounded object using the "highest time-least probability" criterion. The performed simulation is using systematic experimental data obtained from numerous studies of those electrophysical processes that determine the direction of the lightning channel propagation and determine the moment and place in the space of the initial orientation of the leader to the object: the distribution of electric field strength around the top of the leader and in the air gap, return stroke current, the level of the leader channel top potential, change of the leader channel propagation speed, etc. The use of information on the statistical distribution of currents and potentials made it possible to calculate the predicted probability of damage to each section of the object, including side impacts. The calculations showed the possibility of using the proposed methodology to evaluate the effectiveness of a lightning protection system in designing by comparing the probability of hitting a ground object and the average annual number of projected impacts for different lightning protection systems.

Latitude and Topographical Dependence of Lightning Return Stroke Peak Current in Natural and Tower-Initiated Negative Ground Flashes

Experimental data show that the peak currents of first and subsequent lightning return strokes in negative ground flashes increase with decreasing latitude. In this paper, the reason for this dependence of peak return stroke current on latitude is explained using the fact that the height of the charge centers increases with decreasing latitude. Results show that in tropical regions where the height to the negative charge center is about 8 km, the median values of the first and the subsequent return stroke peak currents are about 42 kA and 15 kA, respectively. If the height to the charge center is larger than 8 km, the peak currents will also become larger. For example, if the location of the charge center is increased to about 9 km, the median values of the first and subsequent return stroke peak currents will increase to about 45 kA and 16 kA respectively. The same reasoning shows that, even in the same geographical region, the peak return stroke current may decrease as the elevation of the ground where the lightning strikes take place increases. The results also indicate that the peak subsequent return stroke current in tower-initiated negative lightning flashes decreases as the height of the tower increases. These theoretical predictions are in general agreement with the available experimental data.

Parametric dependence of lightning impulse behavior of grounding electrodes buried in a dispersive and ionized lossy soil under first- and subsequent-stroke currents

Purpose The purpose of this paper is to investigate the simultaneous effects of ionization and dispersion of soil on the impulse behavior of grounding electrodes under first and subsequent stroke currents. Design/methodology/approach A recently introduced technique called improved multi-conductor transmission line (MTL) is simplified for grounding electrodes buried in both-affected soils. Findings The simulation results show that including the two effects simultaneously in highly resistive soils under high-valued subsequent stroke current is recommended. Otherwise, simultaneous effects can be disregard. Originality/value To the best of the authors’ knowledge, there is no research on sensitivity analyses for the simultaneous inclusion of the two effects on the effective length and the induced voltage on the soil surface. To this end, the simplified MTL is applied to the grounding electrodes. The simulation results show that the computational efficiency in comparison with previous methods is, first, considerably increased. Second, the simultaneous effects result in decreasing the soil surface voltage with respect to situations where either ionization or dispersion is taken into account (single-affected soils). In other words, the performance of grounding systems is improved. Third, the effective length in both-affected soil is has a middle value with respect to the single-affected soil. Such findings practically and financially are of importance.

Determination of Cumulative Distribution Function of the Crest Value of the Lightning Current Circulating Through Line Surge Arresters

For the selection and design of line surge arresters (LSA), it is essential to know the characteristics of the lightning current circulating through LSA. When lightning strikes a transmission line, only a part of the lightning current circulates through LSA.This part mostly depends on the point of impact, and the characteristic of the lightning stroke current. The determination of the cumulative distribution function of the lightning current circulating through arresters is presented in first part of the paper. It can be applied on transmission lines where LSAs will be installed to protect the line against the effect of atmospheric discharges.Second part of paper presents the calculation results of the cumulative distribution function of the lightning current circulating through arresters for particular 110 kV transmission line located in an area with high lightning activity.

Digital Signal Processor Based Device for Measurement of Return Stroke Currents of Lightning Strikes to Tall Structures: First Experimental Results

This article describes the features of a device developed for measurement and recording of waveforms of first return stroke currents of lightning flashes striking tall grounded structures. The operation of this device is based on the detection of the voltage induced along a loop by the fast-varying magnetic field produced by the current flowing along the structure close to the device. A digital signal processor supports the data acquisition. The device includes means for remote internet access, self-test, and data transfer. Preliminary laboratory tests consisting of the measurement of impulsive currents intended to resemble first return stroke currents, using both the device and a reference measuring system, were performed. They allowed the analyzing of the source of differences and improving the system performance. After that, the device was installed at Morro Cachimbo Station, Brazil. The waveforms of three first return stroke currents have been recorded since then and the results showed to be consistent with those obtained by the accurate measuring system of the instrumented tower. The application of a network of this low-cost device is worth developing the regional database of lightning current parameters, and providing ground-truth references for calibrating lightning locations systems.

Lightning Protection of Ancient Chola Monument in South India Based on Three-Dimensional Geometric and Electro-Geometric Techniques

Lightning is one of the most commonly occurring natural phenomena which causes irrecoverable damage toedifices which include monuments that uniquely showcase global heritage. Most monuments are usually built tall since these signify symbols of victory, whereby invariably becoming vulnerable to lightning. Though several researchers have implemented various Lightning Protection Systems (LPS) to a considerable level of success, substantial statistical variations in prospective stroke currents during lightning due to factors such as climate change,complexities in geographical topography etc., present considerable challenges in obtaining a common framework for protection of structures. Hence, this research focuses on carrying out analysis based on exhaustive case-studies for an ancient United Nations Educational, Scientific and Cultural Organization (UNESCO) monument in South India. The first objective of this research is in carrying out detailed comparison of shielding effectiveness based on 3D geometric and electro-geometric LPS strategies such as Protection Angle Method (PAM) and Rolling Sphere Method (RSM). The second aims at assessment of risk in accordance with IEC 62305 for estimation of level of risk and the role of varying lightning protection levels utilizing striking distance models to obtain the appropriate choice of the location of air terminal. The third focuses on conducting cross-validation studies to assess the adequacy of the proposed location of LPS using SESShield-3D by depicting the critical zones that necessitate additional protection. In addition, shielding failure analysis of the proposed LPS is also carried out. Inferences on unshielded zones for the three-dimensional (3D) layout models of the monuments have been summarized with appropriate recommendations.

Current Observation Results of Downward Negative Flashes at Tokyo Skytree From 2012 to 2018

Direct observation of lightning current is a fundamental approach to evaluating lightning parameters, which are among the most basic factors for the lightning protection design of various grounded objects. However, for a tall grounded structure, upward lightning flashes initiated from the top of the structure have usually been observed, and the direct observation results of downward flashes have been limited. We developed and installed a pair of Rogowski coils at Tokyo Skytree, which is a 634-m-high freestanding broadcasting tower in Japan (35.71°N, 139.81°E), and have conducted direct observation of lightning flashes striking the tower. As of November 2018, 70 lightning flashes striking the tower, 26 downward and 44 upward, have been observed since the end of February 2012. In this paper, we focus on the downward negative flashes that occurred at the tower for seven years from 2012 to 2018 and report on the observed results of typical waveform parameters of lightning stroke currents in comparison with other observed results on downward negative flashes.