Return Stroke Current Waveform Research Articles

A Procedure to Infer Lightning Return-Stroke Current Waveform From Far-Field Waveform for the Case of Lossy Ground

A Procedure to Infer Lightning Return-Stroke Current Waveform From Far-Field Waveform for the Case of Lossy Ground

Effects of Approximating Recorded Lightning Currents With CIGRE Waveforms on Computed Fast-Front Overvoltages and Critical Lightning Currents Causing Flashover to Overhead Transmission Lines

This work investigates through simulations with the ATP-EMTP program the application of recorded lightning current waveforms to the estimation of fast-front overvoltages and critical lightning currents causing flashover to overhead transmission lines. Typical lines are evaluated with both horizontal (single-circuit) and vertical (double-circuit) phase configurations and AC voltage from 66 kV up to 765 kV. Backflashover as well as shielding failure flashover simulations were performed for several recorded first return-stroke current waveforms of negative downward lightning flashes, as reported in literature. Their approximations with the widely-used CIGRE lightning current waveform were also employed in simulations. CIGRE waveforms, considering the statistical distributions of the front time, maximum steepness, and time to half value, were used as well. A comparison between double-peak waveforms, composed of seven Heidler functions, and their CIGRE approximations is made. The latter generally yield conservative values of overvoltages and critical backflashover currents. The leader development models used for assessing the behavior of insulators and long air gaps under fast-front overvoltages are discussed regarding the criterion for the termination of leader propagation yielding withstand of line insulation.

Differences Between Currents of Triggered Lightning Striking the Distribution Line and the Ground

In this paper, the initial stage and the return stroke current waveform parameters of rocket-triggered lightning flashes to the ground and to the distribution line have been analyzed. The results show that the average current, the charge transferred and the action integral associated with the Initial Stage with return strokes are greater than the corresponding values without return strokes. For the initial stage, the presence of the distribution line greatly reduces the maximum current, average current, charge transfer, and action integral by a factor of 0.35, 0.42, 0.51, and 0.19, respectively. For the return stroke, the presence of the distribution line has little effect on the other parameters except for a 2.4-fold increase in the 10-90% risetime. The presence of the distribution line affects the initial stage parameters more significantly than the return stroke parameters, probably because the lightning channel equivalent impedance of the initial stage is much smaller than that of the return stroke. The lightning channel equivalent impedance of the initial stage estimated in this paper is about 145 ohms and the estimated lightning channel equivalent impedance for the return stroke is greater than 2000 ohms.

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.

Analysis the effect of an ocean-land mixed propagation path on the induced voltage in overhead lines due to inclined lightning

In this paper, the induced overvoltage of the non-vertical lightning channel on the overhead line in the presence of ocean-land mixed propagation is investigated. The lightning-induced voltage was evaluated by using a full-wave approach based on the Finite Element Method (FEM) to solve the Maxwell equations. The influence of channel inclination, strike location (ocean or land), overhead line distance from ocean-land interface, and return stroke current waveform on the induced voltage waveform, the peak of the induced voltage, and voltage profile along the line is investigated. The induced voltage is significantly impacted by the channel inclinations angles, strike location, and distance between line and ocean-land interface. As the overhead line gets closer to the ocean, the induced voltage of the inclined channel in the middle point of the line will be decreased in comparison to the cases the line is far from the ocean. If the inclined lightning passes above the line, increasing the inclination angle will significantly increase the peak and decrease the rising and settling time of the voltage waveform.

Electromagnetic transient modeling of grounding electrodes buried in frequency dependent soil with variable water content

The increasing demand for electricity over the past few decades has been continuously urging for more reliable power systems. Power transmission line networks, due to their vast physical dimensions, are the most critical components of a complex power system concerning the direct lightning strike. Grounding systems are widely used to mitigate the transient overvoltages for the protection of electrical component and human safety. The goal of this paper is to investigate the effect of frequency dependence of soil electrical parameters on the performance of vertical and horizontal grounding electrodes subjected to direct lightning strike, considering a variable water content of soil. Four soil models that take into account the variation of soil water content are reviewed and compared. The numerical simulations are performed using a full-wave electromagnetic model based on the Finite Element Method (FEM) in the frequency range from 1 kHz to 5 MHz and applying different soil models with varying water content. Then, electromagnetic transient (EMT) compatible equivalent circuits of grounding electrodes are developed using Fast Relaxed Vector Fitting (FRVF). Typical first and subsequent return stroke current waveforms measured at two different locations are adopted. The results of this paper demonstrate the importance of considering the variation of soil water content in the transient response of grounding electrodes. Simulation results demonstrate that the frequency dependence of the soil parameters lead to a decrease of the potential rise of the grounding electrodes compared to the case where the soil parameters are assumed constant. The effect of soil water content on the grounding performance is also shown to be dependent on the soil type, value of soil water content, and length of electrode.

Measurement of Return Stroke Current With Magnetic Sensor in Triggered Lightning

Based on the magnetic field recorded with a magnetic sensor deployed at 130-m distance from the channel base, we remotely measured the return stroke current waveform in classical rocket-triggering lightning flashes, including 40 M-components and 48 return strokes (RSs) in eight triggered flashes observed during the summer of 2019. The current waveform retrieved from the close magnetic field is in excellent agreement with the coaxial shunt measurement. For return strokes, the amplitude error of the peak current is less than 1 kA. The error of the 30%-90% risetime is less than 0.1 μs. The error of the half-peak width is less than 1 μs. The error of charge transfer within 0.1 ms of the return strokes is less than 0.1 C. For M-components, the amplitude error of the peak current is about less than 0.3 kA. The error of the 30%-90% risetime is generally less than 4%. The error of the half-peak width is approximately less than 3%. The error of charge transfer within 0.1 ms of M-components is less than 0.02 C. The magnetic sensor is likely applicable to measure lightning current without direct current measurement at near range in rocket-triggered lightning or natural lightning flashes.

Lightning Performance of Transmission Lines: Impact of Current Waveform and Front-Time on Backflashover Occurrence

The influence of the return-stroke current waveform and front-time on the occurrence of transmission-line backflashover was assessed via numerical simulation, using the data of two real lines as examples. The overvoltages resulting from distinct lightning current representations (triangular, CIGRE-concave, and double-peaked waveforms) were calculated using an electromagnetic model. The occurrence of backflashover was assessed applying different flashover criteria. Using robust criteria, in particular, the disruptive effect and leader progression models, leads to similar backflashover probabilities for all waveforms; although the probability resulting from these criteria could be different. Also, it leads to practically the same probability obtained using the median current front-time (3.8 μs) or by varying this parameter within realistic range (1.5–10 μs). This still holds true when a correlation between the front-time and peak current is considered. The conclusions are not valid when applying the voltage–time curve method, as the results yielded by this flashover criterion are affected both by the current waveform and the front-time.

Isolated vs. Interconnected Wind Turbine Grounding Systems: Effect on the Harmonic Grounding Impedance, Ground Potential Rise and Step Voltage

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.

Lightning Performance of Overhead Power Distribution Lines in Urban Areas

Buildings nearby urban overhead power lines are expected to reduce the number of direct strikes to the line conductors and also to attenuate the lightning electromagnetic pulse (LEMP) radiated by indirect lightning strokes. The statistical method described in IEEE Std. 1410 for the lightning performance assessment, as the other methods available in the literature, includes only the former effect. In order to take into account also the latter effect, in this paper, the LEMP attenuation due to the buildings is represented by means of specific weighting functions applied to the LEMP analytical expressions valid for open terrain. For both the cases of ideal and lossy ground, the parameters of the weighting functions are identified through the least-square minimization of the differences with the results provided by a finite-element method model that is assumed as reference for the configurations analyzed. The weighting functions can be used for lightning return stroke current waveform and distances between the line and the stroke location different from those used for their identification with reasonable accuracy. Finally, this paper compares the lightning performances of a power line evaluated with and without the presence of nearby buildings.

Influence of the Return Stroke Current Waveform on the Lightning Performance of Distribution Lines

An accurate evaluation of the lightning performance of overhead power distribution lines, that is, the evaluation of the expected number of annual flashovers, can be obtained by the application of the Monte Carlo method. In order to reduce the computational effort, a simplified waveform of the channel base current is generally assumed, for example, a linearly rising current with flat top. This paper proposes a Monte Carlo approach able to take into account the typical functions adopted to represent the waveform of the lightning current at the channel base (i.e., the Heidler function and the CIGRE function). Moreover, this paper analyzes the effects of different current waveforms on the lightning performance of distribution lines for both direct and indirect strokes.

Volt–Time Curve Prediction of Distribution Insulators Under Standard and Typical Lightning Overvoltages Using the Disruptive Effect Method

Through the development of detection and measurement systems for lightning strokes, the possibility arose for the identification of the characteristic parameters of lightning current and the resulting voltage waveforms that stress the power system insulating equipment. The real lightning voltages that stress the insulation may vary over a wide type of waveforms and may also differ significantly from the standard 1.2/50 $$\upmu \hbox {s}$$ lightning impulse voltage. Therefore, the prediction of volt–time characteristics of any insulating material for such non-standard voltages is required for a proper insulation design. In this regard, this paper aims at evaluating the dielectric behaviour of medium voltage insulators subjected to voltage impulses with standard and non-standard waveforms, by applying the disruptive effect method. The non-standard lightning overvoltage waveforms considered in this study were based on lightning overvoltages produced by real return stroke current waveforms observed on conveyed measurement data. The investigation involves a comparison between measured and predicted voltage-time characteristics of insulators, considering single-peaked and double-peaked non-standard impulsive voltage waveforms as well as the standard lightning impulse voltage. Three different types of insulating arrangement involving 15- and 25-kV pin-type porcelain insulators were investigated. The estimation of the parameters required for this prediction method was performed using a simulation language available at ATP/ATPDraw software called MODELS.

Lightning performance of transmission lines based upon real return-stroke current waveforms and statistical variation of characteristic parameters

This paper presents investigative studies concerning the lightning performance of 500kV transmission lines considering the characteristic parameters of first stroke current observed in measurement data along with its statistical variation. Therefore, advanced electromagnetic models were applied during the development of computational models, thus allowing a realistic representation of the first stroke current waveform. Lightning performance studies were conducted applying two of the most commonly used return-stroke current models, besides the first stroke current model recommended by CIGRÉ. The aim therefore is to identify which of these present the most accurate results, when compared to the use of real return-stroke current waveforms. The volt–time characteristics produced by each of the return-stroke current waveforms were evaluated using both the leader progression model (LPM) and volt–time curve. The breakdown process modelled through LPM is able to represent accurately the physical process established along the perimeter of the insulator strings, during a backflashover event. Analysis of leader length and velocity can reveal the influence of particular characteristics of lightning overvoltage waveform across the insulators produced by different return-stroke current waveforms in the assessment of the lightning performance of a transmission line. The computational modelling developed herein, allows identifying the critical current, the amplitude of the overvoltage that produces the backflashover, and the instant of time that breakdown occurs. The proposed modelling also makes it possible to determine in which insulator string and tower the backflash happens.

電界波形に基づく雷電流波形と電荷量変化の推定精度の実証

To establish effective countermeasures on power facilities against lightning damage, it is necessary to clarify the lightning characteristics such as current parameters at the area of interest. In order to collect lightning current parameters effectively, the authors have observed electric and magnetic field waveforms simultaneously at south Kyushu, where the lightning flash density in summer is high. Based on observed electric field waveforms, the lightning current parameters have been estimated by adopting the Diendorfer-Uman model (DU model) as the return stroke model. In this paper the accuracy of the estimated return-stroke current waveform is verified by comparison with directly measured return-stroke current waveform, along with the accuracy of the estimated charge transfer from the electric field waveform measured with a slow antenna.

Lightning-Induced Current in a Cable Buried in the First Layer of a Two-Layer Ground

This paper analyzes the effect of a two-layer ground on the current induced in the shield of a buried cable due to lightning flashes. Each layer is assumed to be horizontal, homogeneous, isotropic, and having its own electrical parameters: conductivity, permittivity, and permeability. The inducing horizontal electric field is calculated for the incident azimuthal magnetic field and it is used for the calculation of the induced current. The calculation method is validated by comparing its results with results published in the literature. The currents induced in the shield of a buried cable by typical return-stroke current waveforms are calculated. The results show that the induced current waveform is initially determined by the first layer but, for later times, it follows the current that would be induced if the ground was homogeneous and had the characteristics of the second layer.

An Approximate Formula for Estimating the Peak Value of Lightning-Induced Overvoltage Considering the Stratified Conducting Ground

In this paper, we present an improved and extended approximate formula for estimating the peak value of lightning-induced voltages in an overhead line, considering the horizontally stratified conducting ground. The approximate formula proposed in this paper is based on the return stroke transmission-line model (TL) and a trapezoidal lightning return stroke current waveform with the typical representative front time of 3.8 μs and the return stroke velocity of 120 m/ μs according to CIGRÉ and the IEEE Standard 1410 Guide. The extended approximate formula is validated by using the 2-D finite-different time-domain method and Agrawal field-line coupling model. The results show that the proposed approximate formula in this paper is simple and suitable for estimating the lightning-induced voltage peak value considering the horizontally stratified ground with satisfied accuracy.

Flashover Rate of 6.6-kV Distribution Line Due to Direct Negative Lightning Return Strokes

The overvoltage associated with direct lightning hits has been the important factor for the insulation design of a 6.6-kV distribution line in Japan. In this paper, the flashover rate of the distribution line associated with direct lightning hits is investigated based on numerical calculations and statistical analysis by taking into account the correlation between the peak and the front duration of negative return-stroke current waveforms. When the line is equipped with surge arresters at the interval of 100 or 200 m in addition to the overhead ground wire, the flashover rate associated with subsequent strokes is higher than that associated with first strokes. This demonstrates the importance of the study of current parameters for subsequent strokes. To obtain a conservative estimate of the flashover rate of a line with surge arresters installed every 100 m, calculated for the variable front duration, it is necessary to assume a constant front duration of less than 4 μs and 0.9 μs in the cases of first and subsequent strokes, respectively. With the increase of the installing interval of surge arresters, a constant front duration, leading to a conservative estimate, increases.

Cn Tower Lightning Return-Stroke Current Simulation

Different functions have been used to model the lightning return-stroke current with the aid of direct current measurements at tall structures. In this paper, a comparison between the Pulse function and Heilder function is carried out to find out the suitability of each of these functions for simulating the lightning return-stroke current, measured at the CN Tower. An automated system for determining the CN Tower lightning return-stroke current waveform parameters is introduced. The curve fitting technique of this system and the estimation of the initial values of the simulation function parameters are presented. An artificial lightning signal, free of noise and reflections, is used as a reference signal for evaluating the parameter extraction system. Finally, cumulative statistics of the CN Tower lightning return-stroke current waveform parameters (peak, maximum rate of rise, risetime, pulse width, decay time and charge) are derived using the Pulse function parameters.

The Peak Value of Lightning-Induced Voltages in Overhead Lines Considering the Ground Resistivity and Typical Return Stroke Parameters

This paper presents an approximate formula for the peak value of lightning-induced voltages in an overhead line, considering the ground resistivity and a trapezoidal lightning return stroke current waveform with typical parameters 3.8-μ s front time and 120-m/μ s velocity. It presents an improvement in a formula previously proposed by the authors. The formula is used with a probabilistic approach, and the results are compared with theoretical and experimental results available in the literature. The results show that the proposed formula, although very simple, is in good agreement with results obtained using complete formulations and experimental data.

Flashover Rate of Distribution Line Due to Indirect Negative Lightning Return Strokes

The flashover rate of a distribution line associated with indirect lightning flashes is investigated based on numerical calculations and statistical analysis by taking account of the correlation between the peak value and the front duration of negative return-stroke current waveforms. When the grounding interval of an overhead ground wire and/or surge arresters is 200 m, surge arresters are more effective than an overhead ground wire in suppressing flashover of the power lines, and installation of both is very effective. The flashover rate decreases if there is correlation between the peak and the front duration of lightning current; and it significantly decreases with the increase of the ground conductivity. When the line is equipped with surge arresters only, the flashover rate associated with subsequent strokes is higher than that associated with first strokes; and calculation with the fixed front duration of 2 mus for first stroke current does not always result in good estimates of flashover rate.