Lightning Return Stroke Current Research Articles

Observation of Overvoltage at the Terminal of 10 kV Distribution Line by Direct Triggered Lightning

This paper reports the waveform characteristics and parameters of the overvoltage at the terminal of a 1.5 km 10 kV distribution line by direct triggered lightning. The three-phase overvoltage exhibited three kinds of waveforms, all including the initial rising process of the negative peak, the transition from negative peak to the positive peak or the residual voltage, and the subsequent oscillation process. It is observed that the negative peak value of the three-phase overvoltage is between −8.2 kV and −96.1 kV and the rise time of negative peak is between 3.2 μs and 31.7 μs, while the corresponding peak value of the return stroke current is between 3.3 kA and 32.9 kA. When the return stroke current is relatively small, the negative peak value of the direct struck phase overvoltage is twice or more than that of the indirect struck phase. When it is larger, the negative peak value of the indirect struck phase overvoltage is much closer to that of direct struck phase. There is good linear relation between the negative peak value of the indirect struck phase overvoltage and the peak value of the lightning return stroke current, with correlation coefficient being 0.98 and 0.90.

Influence of the Distribution of Lightning Strikes Along the Span of Transmission Lines On Their Backflashover Rate: The Span Factor

The effect of the distribution of lightning strikes along the span on the performance of transmission lines was assessed following an advanced methodology, based on a Monte Carlo approach. First, considering typical features of 138-kV and 230-kV transmission lines, systematic simulations were performed, using an electromagnetic model to determine overvoltages and the disruptive effect method to assess backflashover occurrence. The influence of five variables was analyzed (tower-footing impedance, span length, waveform of the lightning return stroke current, insulation withstand and model of lightning attractiveness). The results indicated that a span factor is able to properly express the effect of the strikes distribution in the span and revealed trends: larger span factor with increasing tower-footing impedance and longer span length, smaller span factor with increasing critical flashover overvoltage and larger span factor for those models that assume larger attractiveness of the transmission line tower. Considering realistic distributions of tower-footing impedance along the line, a very narrow dispersion of the span factor was found. Assuming the same attractiveness for towers and shield wires, values of the span factor of about 0.8, 0.56, 0.53, and 0.37 were found, respectively for the 138-kV, 230-kV, 345-kV and 500-kV transmission lines.

Investigating the effect of lightning channel inclination on the induced voltage in overhead lines in the presence of horizontally stratified ground

The present paper explores the impact of inclined lightning on the induced voltage on an overhead line in the presence of two-layer horizontal stratified ground. The Finite Element Method (FEM) is utilized to solve the full-wave Maxwell equation and evaluation the induced voltage. The impact of thickness of the top soil layer, upper soil conductivity, and return stroke current waveform on the peak of the transient induced voltage, induced voltage waveform, and profile of the transient voltage along the line is studied. The peak of induced voltage and waveform is remarkably influenced by the angle of the channel, soil structure, and upper soil thickness and conductivity. The results shown where the upper soil layer is less conductive than lower soil, the upper soil layer thickness is an important parameter that influenced the voltage peak. Also, the transient induced voltage peak in the presence of two-layer stratified ground is significantly affected by the lightning return stroke current. When the lightning current has a faster rising and settling time, it could be concluded that channel inclination has a greater influence on the induced voltage in the presence of two horizontal stratified layers.

Three‐phase overvoltage at lightning strike point due to direct triggered lightning to the phase wire of 10 kV power distribution line

This paper reports the observation results of three-phase overvoltage at the lightning strike point of a 1.5 km, 10 kV power distribution line that was struck directly by rocket triggered lightning to its phase wire C. The arrester of the direct struck phase at the lightning strike point operated in all return strokes corresponding to return stroke current from −3.3 kA to −32.9 kA. The waveform of direct struck phase includes an initial spike before negative peak, operation area of metal oxide varistor, and the final attenuation with oscillation. The overvoltage waveforms of the indirect struck phase at the lightning strike point show a small initial negative peak, rapid transition to a large positive peak, and the final negative attenuation with oscillation. The negative peak value of the indirect struck phase at lightning strike point ranged from −4.1 kV to −25.2 kV and that of the direct struck phase was between −78.1 kV and −167.8 kV. The positive peak value of indirect struck phase was between 0.2 kV and 49.8 kV. The negative peak value, zero-crossing time and the peak-to-peak value of voltage all have a good linear relation with the peak value of lightning return stroke current.

Difference in Lightning Current Estimated by Lightning Location System Between Triggered Lightning to Ground and Distribution Line

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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s, and that of triggered lightning to ground is 0.27 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s. Clarification of this underestimation phenomenon is beneficial for the application of the lightning location system in power systems.

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.

An Application of Fractal-Based Lightning for SFR Calculation of High Voltage Substations

Objectives: To simulate the lightning more close to reality and investigate the performance of the lightning protection system of high voltage substation. Methods/Statistical Analysis: The method which is used for the system analysis is a new fractal-based model of simulated lightning by which the zigzag movement of lightning downward leader as well as branching nature is simulated. A new charge distribution is proposed for branched lightning channel. In addition, the branch fading during the lightning downward movement is also simulated in order to simulate the lightning more close to the reality. Findings: The results of the simulated lightning using the proposed method show that the proposed fractal method simulates the lightning close to the reality. The striking distances of a transmission line structure for different lightning return stroke currents are obtained by the proposed method and compared to those of Electrogeometric Model (EGM) and Leader Progression Model (LPM). The results show that how the proposed method obtains a wide range of possible results statistically. The lightning shielding system performance of a practical high voltage substation is investigated based on the proposed model in two different scenarios by which the effect of substation instruments on the lightning protection system is investigated. The results reveal that the presence of the substation instruments completely affects the shielding system performance. Using the propose method, the random behavior of the lightning is well modeled and the shielding failure of the protection system is investigated in a statistical manner. The obtained results are compared to those of EGM, and LPM. The results are discussed and superiority of the proposed simulated lightning model is concluded. Application/ Improvements: The proposed method simulates the different features of the lightning including 1- branching nature, 2- zigzag movement, 3- random behavior, 4- branch fading, 5- branched charge distribution.

Validation and revision of far-field-current relationship for the lightning strike to electrically short objects

In this paper we have validated and revised the general expressions for far-field-current factors presented by Bermudez et al. (2005, 2007) for lightning strike to tall objects on perfectly and finitely conducting ground, respectively. For the perfectly conducting ground, it is found that when the risetime of lightning return stroke current (RT) is larger than 5h/c (h is the height of tall object and c is the light speed), the overestimation caused by the traditional method predicting the lightning current peak is within 10% beyond a distance of 20km from the lightning channel, and with the decrease of observed horizontal distance d, the error will increase due to the effect of induction field component. For example, when d is 10km, the overestimation is about 20% for strike to a 300-m-tall object. For the finite conductivity ranging from 0.01S/m to 0.001S/m, when the lightning strikes the 300-m-tall object, the lightning current peak predicted from the measured magnetic field peak according to the traditional method is overestimated ranging from about +5% to +20% (positive means overestimation while negative means underestimation) and the derivation value is more within a distance of 20km because of induction field component; When the lightning strikes the 50-m-tall object, the predicted current peak according to the traditional method has an error ranging from about +5% to −15%.

On the peak amplitude of lightning return stroke currents striking the sea

Data gathered from the US National Lightning Detection Network (TM) (NLDN) show that the peak currents of lightning flashes striking the sea are significantly higher than those of lightning flashes striking the land. We suggest that the unfavorable conditions for the formation of positive charge pockets in maritime clouds lead to lightning initiation at higher cloud potentials compared to their land counterparts, resulting in larger peak currents in negative lightning flashes striking the sea. As the positive charge pocket does not promote positive ground strokes, no such discontinuity should be expected in positive first return strokes to ground between land and sea.

Considering on the Ground Reflection Effect on the Electromagnetic Fields due to Lightning Channel

Lightning electromagnetic fields are important issues for the evaluation of lightning induced overvoltage on power lines and for setting the appropriate protection level for power networks. Such electromagnetic fields are strongly dependent on lightning return stroke currents at different heights along the lightning channel. On the other hand, the ground reflection factor due to the difference between the return stroke channel impedance and the equivalent ground impedance at channel base can have an effect on the shape of the return stroke currents by entering additional reflected currents into the channel. In this paper, the effect of the ground reflection factor on the return stroke currents at different heights along a channel and the electromagnetic fields associated with the lightning channel at close distances are considered. Moreover, the behavior of the electromagnetic fields versus the reflection factor changes and the radial distance changes are considered and the results are discussed accordingly. The results illustrate that the reflection factor has a direct relationship with the values of the electromagnetic fields while this is usually ignored in earlier studies.

EVALUATION OF LIGHTNING RETURN STROKE CURRENT USING MEASURED ELECTROMAGNETIC FIELDS

The lightning return stroke current is an important parameter for considering the efiect of lightning on power lines. In this study, a numerical method is proposed to evaluate the return stroke current based on measured electromagnetic flelds at an observation point in the time domain. The proposed method considers all fleld components and the full wave shape of the current without the use of a special current model as a basic assumption compared to previous methods. Furthermore, the proposed algorithm is validated using measured flelds obtained from a triggered lightning experiment. The results show a good agreement between the simulated fleld based on the evaluated currents from the proposed method and the corresponding measured fleld at a remote observation point. The proposed method can determine current wave shapes related to a greater number of lightning occurrences compared to the direct measurement of the current.

EVALUATION OF LIGHTNING CURRENT AND VELOCITY PROFILES ALONG LIGHTNING CHANNEL USING MEASURED MAGNETIC FLUX DENSITY

In this paper, an inverse procedure algorithm is proposed in the time domain to evaluate lightning return stroke currents along a lightning channel using measured magnetic ∞ux density at an observation point while the current velocity along a lightning channel is assumed to be a height dependent variable. The proposed method considers all fleld components and it can evaluate the full shape of currents and the current velocity at difierent heights along a lightning channel. Moreover, a sample of measured magnetic ∞ux density from a triggered lightning experiment is applied to the proposed algorithm and the evaluated currents and current velocities are validated using a measured channel base current and magnetic ∞ux density at another observation point.

Influence of Building Structures on the Lightning Return Stroke Current

This paper addresses the influence of building structures on the lightning return stroke current. An equivalent circuit model of the lightning channel is set up using the coupled ¿-type circuit. This model is then integrated with the building structure via the lightning attachment and the mutual coupling. With this integrated circuit model, the lightning current in the building is evaluated using EMTP. It is found that the building generally behaves like a transmission line at its rooftop and on the ground. The rooftop current is the result of the incident lightning current and its subsequent reflected currents on the ground. The propagation parameters of the building can be determined numerically using the integrated model. These parameters vary with the structure type, size, and others. In general, the impedance of typical buildings lies between the channel impedance and grounding impedance, and the lightning current on the lower floors is higher. It is also found that excluding the mutual coupling in the integrated circuit model alters the waveform of the lightning current.

On return stroke currents and remote electromagnetic fields associated with lightning strikes to tall structures: 2. Experiment and model validation

In this paper, simultaneous GPS time‐stamped measurements of the electric and magnetic fields at three distances and of the return stroke current associated with lightning strikes to the Toronto CN Tower (553 m) during the summer of 2005 are presented. The lightning return stroke current was measured using a Rogowski coil installed at a height of 474 m above ground level (AGL). The vertical component of the electric field and the azimuthal component of the magnetic field were measured simultaneously at distances of 2.0 km, 16.8 km, and 50.9 km from the CN Tower. The propagation path from the CN Tower to the first two stations (2.0 and 16.8 km) was along the soil and through the Toronto city, whereas for the third location (50.9 km) the propagation path was nearly entirely across Lake Ontario. The waveforms of the electric and magnetic fields at 16.8 km and 50.9 km exhibit a first zero crossing about 5 μs after the onset of the return stroke. This early zero crossing is part of a narrow undershoot. For fields at 50.9 km the expected zero crossing at about 40 μs is also observed. Metallic beams and other conducting parts in buildings on which electric and magnetic field sensors were located cause an enhancement effect on the measured fields. Although an enhancement can be identified both on the electric and the magnetic fields, the degree of enhancement is actually more significant for the electric field than for the magnetic field. It is shown that the value of the wave impedance (E‐field peak to H‐field peak ratio) could give an estimate of the enhancement effect of the building on the electric field. Propagation effects (decrease of field amplitude and increase of its risetime) can also be observed in experimental records. It is shown that the fields at 50.9 km are less affected by such attenuation, compared to those at 16.8 km, presumably because the path of propagation is mostly across Lake Ontario. Measured waveforms are compared with theoretical predictions obtained using the five engineering return stroke models extended to include the presence of the strike object, namely, transmission line (TL), modified transmission line (MTLL and MTLE), Bruce‐Golde (BG), and traveling current source (TCS) models. A reasonable agreement is found with all five engineering models for the magnetic field waveforms at the three considered distances, although the peak values of the computed fields are systematically about 25% lower than measured values. None of the models was able to reproduce the early zero crossing and the narrow undershoot. As far as the electric field is concerned, larger differences have been observed between simulations and measurements. This may be due to the fact that the enhancement effect of the building on the electric field is stronger than that on the magnetic field. The expression relating current and field peaks associated with strikes to tall structures is also tested versus obtained sets of experimental data. The overall agreement between the theoretically predicted and the experimentally observed field‐to‐current ratio is reasonable, although the formula of Bermudez et al. (2005) appears also to underestimate the experimentally measured ratio (by about 25%). This may be due, at least in part, to the enhancement effect of the buildings on which the field measurement antennae were installed.

Analysis of Effect of Resistive Lightning Protection Terminal on Lightning Return Stroke Current

A study was conducted on the effect of resistive lightning protection terminals in mitigating the lightning return stroke current. The investigation was performed on the recently developed R-L-C circuit model which allows resistive lightning protection terminals to be represented easily as circuit elements. The results show that the peak of the return stroke current was significantly reduced, thus demonstrating efficacy of the resistive lightning protection terminal and the utility of the R-L-C circuit model in such studies.

Far-Field–Current Relationship Based on the TL Model for Lightning Return Strokes to Elevated Strike Objects

New general expressions relating lightning return stroke currents and far radiated electric and magnetic fields are proposed, taking into account the effect of an elevated strike object, whose presence is included as an extension to the transmission line (TL) model. Specific equations are derived for the case of tall and electrically short objects. The derived expressions show that, for tall structures (when the round-trip propagation time from top to bottom within the tower is greater than the current zero-to-peak risetime), the far field is enhanced through a factor with respect to an ideal return stroke initiated at ground level. The enhancement factor can be expressed in terms of the return stroke wavefront speed v, the speed of light in vacuum c, and the current reflection coefficient at the top of the elevated strike object. For typically negative values of this top reflection coefficient, lightning strikes to tall towers result in a significant enhancement of the far electromagnetic field. Expressions relating the far electromagnetic field and the return stroke current are also presented for electrically short towers and for very long return stroke current wavefronts. For the case of return strokes initiated at ground level (h=0), these expressions represent a generalization of the classical TL model, in which the reflections at the ground are now taken into account. We describe also simultaneous measurements of return stroke current and its associated electric and magnetic fields at two distances related with lightning strikes to the 553-m-high Toronto Canadian National (CN) Tower performed during 2000 and 2001. The derived expressions for tall strike objects are tested versus obtained sets of simultaneously measured currents and fields associated with lightning strikes to the CN Tower, and a reasonable agreement is found. Additionally, it is shown that the peak of the electromagnetic field radiated by a lightning strike to a 553-m-high structure is relatively insensitive to the value of the return stroke velocity, in contrast to the lightning strikes to ground.

Radiation belt electron precipitation fluxes associated with lightning

In this study we consider the dependence of precipitation fluxes arising from whistler‐induced radiation belt losses on the strength of the associated lightning's return stroke current. As a result of this work, it will be possible to use lightning activity data sets to estimate globally induced precipitation flux rates and thus determine the lightning‐induced effect on the radiation belts more accurately. Four study days were selected, during which a high proportion of the lightning activity occurring near the east coast of North America produced observable Trimpi effects on VLF transmitter signals propagating in the region of the Antarctic Peninsula (∼L = 2–2.5). The lack of lightning in Antarctica gives this location a unique advantage for this study. The functional dependence of the relative scattered field amplitude with the return stroke peak current of the lightning discharge suggests that during these events diffusion conditions are occurring near the precipitating radiation belt particles loss cone due to strong whistler wave fields, probably caused by ducted signals. The range of observed Trimpi scatter amplitude of −10 to −35 dB was produced by precipitation bursts with energy fluxes estimated to range over 6.5–0.4 × 10−3 ergs cm−2 s−1. The largest fluxes were found to be driven by lightning currents of about 250 kA, while the smallest detectable fluxes relate to lightning currents of 70 kA. Although 3 of the 4 study days showed a high degree of consistency between the levels of lightning return stroke peak current required to produce any given perturbation scatter amplitude value, conditions were significantly different on 23 April 1994. On this day, observed Trimpi signatures were 6–7 dB greater for any given lightning intensity than on the other study days. These events are consistent with a significantly harder radiation belt precipitation spectra, probably caused by geomagnetic storm‐time acceleration processes of radiation belt electrons.

Modeling of Lightning Return Stroke Current With Inclusion of Distributed Channel Resistance and Inductance

This paper describes the development of a new model for determining lightning return stroke current. An RLC circuit model was formulated to represent the lightning channel and was used to produce the return stroke current at ground matching median recorded values, while keeping reference to the current waveshape in the DU model. The proposed model was shown to be capable of matching the peak current, maximum di/dt, and front duration.

Currents and radiated electromagnetic fields in lightning strikes to tall structures

The paper presents recent developments in the study of lightning discharges - electrical transient components of a thunderstorm - striking elevated objects. In the computation of lightning return stroke currents, we analyze the disturbance introduced by the elevated strike object. A new methodology in lightning return strike modeling is proposed, and applied in the computation of lightning electromagnetic fields at far distances. We compared the resulting expressions with experimentally-measured lightning currents and electromagnetic fields observed at the CN Tower Research Center in Toronto, and found a reasonable agreement. The expressions can be used to calibrate the performance of lightning location systems in cases where lightning currents are measured directly on instrumented towers.

Determination of reflection coefficients at the top and bottom of elevated strike objects struck by lightning

In this paper, we present an analysis of lightning return stroke currents along an elevated strike object. We derive closed form expressions, both in the frequency domain and in the time domain, to calculate the lightning current at any height along a strike object taking into account reflections at the top and at the bottom. The frequency dependence of reflection coefficients is taken into account. We also derive an expression to calculate the reflection coefficient as a function of frequency at the bottom of the lightning strike object from two currents measured at different heights along the strike object. We show that, if the current and its time derivative overlap with reflections at the top or bottom of the strike object, it is impossible to derive the reflection coefficient at the top of the strike object exactly from any number of simultaneous current measurements. We propose an extrapolation method to estimate this reflection coefficient. We propose a second method to calculate the top reflection coefficient from just one current derivative measurement if the current derivative and its reflections do not overlap significantly. We apply the proposed methodology to experimental data obtained on Peissenberg Tower (Germany) consisting of lightning currents measured at two heights. The results suggest that the reflection coefficient at ground level can be considered as practically constant in the frequency range 100 kHz to 800 kHz. Although the estimated ground and top reflection coefficients are in good overall agreement with values found in the literature, the estimated values for the top reflection coefficient from the extrapolation method are somewhat lower than those found employing the current derivative method; the differences are discussed.