Indirect Lightning Research Articles

Electrical Performance of Polymer-Insulated Rail Brackets of DC Transit Subjected to Lightning Induced Overvoltage.

The fourth rail transit is an interesting topic to be shared and accessed by the community within that area of expertise. Several ongoing works are currently being conducted especially in the aspects of system technical performances including the rail bracket component and the sensitivity analyses on the various rail designs. Furthermore, the lightning surge study on railway electrification is significant due to the fact that only a handful of publications are available in this regard, especially on the fourth rail transit. For this reason, this paper presents a study on the electrical performance of a fourth rail Direct Current (DC) urban transit affected by an indirect lightning strike. The indirect lightning strike was modelled by means of the Rusck model and the sum of two Heidler functions. The simulations were carried out using the EMTP-RV software which included the performance comparison of polymer-insulated rail brackets, namely the Cast Epoxy (CE), the Cycloaliphatic Epoxy A (CEA), and the Glass Reinforced Plastic (GRP) together with the station arresters when subjected by 30 kA (5/80 µs) and 90 kA (9/200 µs) lightning currents. The results obtained demonstrated that the GRP material has been able to slightly lower its induced overvoltage as compared to other materials, especially for the case of 90 kA (9/200 µs), and thus serves better coordination with the station arresters. This improvement has also reflected on the recorded residual voltage and energy absorption capacity of the arrester, respectively.

Impact of Grounding Modeling on Lightning-Induced Voltages Evaluation in Distribution Lines

Lightning-induced voltages are one of the main causes of shutdown in distribution lines. In this work, attention is focused on the effects of wideband modeling of electric grounding in the overvoltage calculation along insulator strings due to indirect lightning strikes. This study is done directly in the time-domain with the grounding being represented with an equivalent circuit accounting for its dynamics. Results show that the adoption of commonly adopted simplified grounding models, such as low-frequency resistance, may lead to an underestimation of the overvoltage. According to the results, differences in the order of 25% can be found in some studied cases.

On the Influence of Dielectric-Coated Conductors on the Performance of Three-Phase Compact Distribution Lines Against Indirect Lightning Strikes

This article presents an investigation on the performance of a three-phase compact distribution line against nearby lightning strikes. It is shown that neglecting the insulating layer that surrounds the phase conductors as usually done in this type of study does not significantly change voltages induced from phase to ground, but can have some effect on voltages induced between phase and messenger, which are the ones that effectively stress the insulation. However, the observed differences are strongly minimized if the usual practice of grounding messenger and neutral in regular intervals of less than 200 m is considered. This is confirmed by a Monte-Carlo-type study that shows that the failure rate of the line is not affected by the inclusion of the insulating layer that surrounds the phase conductors in practical conditions.

Quantification of the Indirect Lightning Using FIT Analysis Under Soil Nonuniformity

One of the phenomena affecting the insulation coordination of power distribution systems is indirect lightning. This article aims to investigate the impacts of stratification of the soil along with the characteristics of the lightning current, i.e., peak, current time-derivative, striking distance to overhead lines on quantification of the lightning indirect overvoltage (LIOV). Accordingly, comprehensive analyses have been established based on the finite integration technique. The flexibility of the method and the simulation results have been compared with the other finite element method and well-known formula, i.e., Rusck and Darveniza. It is also demonstrated that the Darveniza's formula cannot be relied upon as a precise approach in nonuniform grounds. It is revealed that more resistivity of the lower layer results in the increase of LIOV peak in a two-layer soil. It is comprehended that the increase in the number of layers could highly affect LIOVs. Furthermore, the results indicate that the nonuniformity of the ground increases the sensitivity of LIOV to the characteristics of lightning strokes. Finally, an intelligent package is introduced to assess the characteristics of the indirect lightning-induced overvoltage in the complex situation within acceptable accuracy and computation time based on an equivalent resistivity of the soil.

Effect of Rusck's Approximation on the Indirect Lightning Performance Assessment of Aerial Power Lines

This article investigates the effect of a simplified procedure, referred here as Rusck's approximation, which consists in obtaining the electrical potential at a given height by multiplying the vertical electric field computed at ground surface by the height considered, instead of integrating the vertical electric field from the ground surface up to the given height. This procedure is currently considered by several authors but, so far, has not been investigated in detail. The article shows that this approximation leads to significant deviations at close range from the strike but provides accurate results if the distance from the strike is higher than three times the height of the point considered. The article also shows that the distance between the line and the flash must be higher than three times the line height to obtain lightning induced voltage peak-values sufficiently high to produce line flashovers, as otherwise the flash will strike the line directly. As Rusck's approximation provides accurate results under such condition, it can be used for the assessment of indirect lightning performance of aerial power lines without any significant loss of accuracy.

Overhead transmission line performance with respect to grounding impedance on alpine terrain

The present paper shows a study case of transient effects of direct and indirect lightning discharges on overhead transmission lines with respect to actual grounding impedances of the transmission line system. The transient measurement data was gathered from two 400 kV double-system overhead lines equipped with an overhead ground wire. Additionally installed RC dividers are used to perform transient voltage measurements with high accuracy in amplitude and frequency. The pairing of electric, time and geographic parameters of the used datasets provides the basis for an analysis of the performance of the overhead lines and the high-voltage system influenced by lightning discharges. For this case study, a novel approach is presented where the actual tower-footing grounding impedance of the two systems is related to the transient effects of direct and indirect lightning discharges on the lines as new parameter. The topic, whether it be exposed overhead transmission line systems in the alpine area or line sections with high grounding impedances that show a higher probability of power system faults, is analysed and interpreted in this case study. The results show no correlation between tower exposure (mountainous or flat terrain) and lightning discharge frequency. For the correlation of the tower footing grounding impedance with the recorded transient measurements, no accumulation of transient effects at towers with higher grounding impedance can be observed either. Regarding the analysed dataset, a high reliability of supply can be expected for systems with a similar setup and comparable lightning parameters. Grounding concepts of existing overhead lines can be validated by these results.

Enhancing the Protective Performance of Surge Arresters against Indirect Lightning Strikes via an Inductor-Based Filter

Preventing the medium voltage (MV) transformer fault by protecting transformers against indirect lightning strikes plays a crucial role in enhancing the continuous service to electricity consumers. Surge arresters, if selected properly, are efficient devices in providing adequate protection for MV transformers against transient overvoltage impulses while preventing unwanted service interruptions. However, compared to other protective devices such as the spark gap, their prices are relatively high. The higher the surge arrester rating and energy absorption capacity are, the higher the prices go. This paper proposes an inductor-based filter to limit the energy pushed into the surge arrester, and consequently to prevent any unwanted failure. An energy-controlled switch is proposed to simulate the fault of the surge arrester. Surge arresters with different ratings, e.g., 12 kV, 18 kV, 24 kV, 30 kV, 36 kV, and 42 kV with two different classes of energy, namely, type a and type b, are tested under different indirect lightning impulses such as 100 kV, 125 kV, 150 kV, 175 kV, 200 kV, 250 kV, 300 kV, and 500 kV. Furthermore, these surge arresters are equipped with different filter sizes of 100 μH, 250 μH, 500 μH, and 1 mH. Results prove that equipping a surge arrester with a proper filter size enhances the performance of the surge arrester significantly such that a high rating and somewhat expensive surge arrester can be replaced by a low rating and cheap surge arrester while providing similar or even better protective performance for MV transformers. Therefore, such configurations not only enhance the protective capability of surge arrester, but also reduce the planning and operating costs of MV networks.

Direct Lightning Flash Protection of Satellite Antenna

It will cause some problems like improper way of lightning protection and improper height of lightning rod in the design for direct lightning flash protection of satellite antenna, which may increase the probability of lightning strike, due to the lack of express provisions in relevant standards about satellite antenna lightning protection level and direct lightning flash protection ways. A way was presented for the determination of lightning protection level based on probability and risk assessment of lighting through a specific instance, by comparing the probability of lightning, costs and difficulties for construction between two different types of lightning protection ways under the same conditions for indirect lightning protection, an appropriate way was proposed for direct lightning flash protection by using lightning rod installed on the satellite antenna.

Grounding System Modeling and Evaluation Using Integrated Circuit Based Fast Relaxed Vector Fitting Approach, Considering Soil Ionization

Since high voltage transmission line towers or wind turbines structures are installed in high-altitude areas, it is essential to achieve a high overvoltage protection system against direct and indirect lightning strikes collisions. The lightning current must be discharged quickly into the protective earth, to prevent the dangerous over-voltages formation and define a reference voltage node. This paper presents a novel model to assess the behavior of the grounding system, based on Pocklington integral equations under lightning magnetic fields and variations in soil ionization, in which an explicit circuit-based vector fitting RLC admittance branches are proposed. The frequency-dependent behavior of grounding system frequency response and soil ionization effect is modeled in time domain, straightly to implement into the electro-magnetic transient program (EMTP). The model verification contains horizontal, vertical, and their combinations of grounding grids to represent the complete investigations under lightning strikes. The harmonic impedance mathematical formulations and principles are derived based on a rational function, that could be applicable on ground potential rise (GPR) investigation.

Corona Effect Influence on the Lightning Performance of Overhead Distribution Lines

Overhead distribution lines can be seriously damaged from lightning events because both direct and indirect events can cause flashovers along the line. The lightning performance of such power lines is usually computed neglecting the effect of corona discharge along the conductors: in particular, the corona discharge determined by the indirect lightning event is taken into account only by few researchers because it can have meaningful impacts only in few cases. However, when we deal with overhead distribution lines with high Critical Flashover value (CFO) and small diameters, the corona discharge caused by indirect events has to be taken into account. This paper shows the effects of corona discharge in the lightning performance computation of overhead distribution lines. The analysis will involve different configurations in terms of line diameter and air conditions, focusing on the negative effect of corona discharge in the number of dangerous events that determine line flashovers.

Enhancing the lightning performance of overhead transmission lines with optimal EGLA and downstream shield wire placement in mountainous areas: a complete study

Service unavailability of transmission lines, particularly in mountain areas due to the direct and indirect lightning strikes, is considered as a challenging issue within electric companies. Therefore, the efforts to mitigate the power outages caused by this phenomenon have been introduced. In this study, an attempt has been made to study the different types of externally gapped line arresters (EGLAs) considering the Pinceti model and discharge voltage curve. Based on the best selected EGLA, the installation effect of EGLA on the possibility of instance back-flashover in different phases of the transmission line is investigated in the presence of downstream shield wire. For assessment, a double-circuit 400 kV transmission line in a mountainous area is modelled in EMTP-RV software. Then, an extensive analysis is carried out to verify the effectiveness of this method. The obtained results show the acceptable transmission line direct lightning protection can be achieved by four EGLAs in upper and middle phases with downstream shield wire. Although employing the downstream shield wires in the transmission line imposes more costs, but by using them, the scale and capability of EGLAs can be reduced.

An accurate approach for the evaluation of the performance of overhead distribution lines due to indirect lightning

The probability of flashovers due to indirect lightning on overhead lines is us ually calculated assuming a statistical distribution for the induced voltages, and a deterministic and specified value for the insulation level of the line. However, more accurate practices of insulation coordination suggest a statistical treatment for the insulation level too, in order to relate the probabilistic nature of both electrical stress (induced voltage) and the electrical strength (insulation level). In this paper, a statistical insulation coordination method is applied for the assessment of induced-voltage flashovers and, more in general, for the indirect lightning performance of the line. Such a statistical approach, which is inherently more accurate than the traditional approach, allows also to discriminate among probability of occurrence of flashovers on one, two, or on all phases.

Impact of Frequency-Dependent Soil Models on Grounding System Performance for Direct and Indirect Lightning Strikes

The goal of this article is to investigate the effect of frequency-dependent soil models on the performance of grounding electrodes subjected to lightning strikes. Several soil models are examined while accounting for the variation of soil resistivity and permittivity as a function of the lightning current frequency spectrum. The analysis is performed for a homogeneous soil and a two-layer horizontally stratified soil. The impact of the frequency-dependent soil parameters on the ground potential rise (GPR) of simple grounding electrodes subjected to lightning is analyzed and discussed. The analysis is performed in the frequency domain and in the time domain. A wind turbine and its grounding system are also considered in this article. Special attention is given to the case of indirect lightning, rarely mentioned in the literature. The GPR of the grounding electrodes is examined when the frequency dependence of the soil is taken into account and the lightning channel is located at close distances to the electrodes. Indeed, the level of induced electromagnetic fields caused by a nearby lightning channel can still be too high and potentially dangerous. The computations are performed using an efficient Method of Moments (MoM) numerical tool based on surface-wire integral equations for a stratified medium in the frequency range from dc to several MHz. Numerical results demonstrate that the frequency dependency of the soil parameters results in a decrease of the potential rise of the grounding electrodes, with respect to the case where the parameters are assumed constant.

Stimulatory growth effect of lightning strikes applied in the vicinity of shiitake mushroom bed logs

Since ancient times, the anomalous occurrence of mushrooms has been observed in and around locations struck by lightning. Based on this phenomenon, various cultivation techniques using a high voltage to cultivate shiitake mushroom in bed log (wood) have been proposed. Undoubtedly, the fruiting capacity of shiitake mushrooms is significantly promoted by direct application of a high voltage to the cultivation bed logs. However, mushroom bed logs are rarely struck directly by lightning in the natural environment. Thus, it is important to devise a stimulation method that matches conditions in the natural environment. In this study, we performed experiments involving indirect lightning strikes using a new method that mimics the natural environment as closely as possible. Specifically, we used the electric discharge created by an impulse voltage generator to create lightning but did not apply it directly to the cultivation bed log. Instead, the cultivation bed logs were placed a few meters away from the lightning rod. Subsequently, the fruiting capacity of the shiitake mushrooms with and without the indirect lightning strikes was compared. The experimental results indicated that, with the indirect lightning strikes, the extent of shiitake fruiting almost doubled compared to the case without the indirect lightning strikes. Furthermore, the results confirm that an increased shiitake mushroom production is possible using lightning strikes, even if the associated high voltages are not applied directly to the bed logs.

Corona lightning overvoltage analysis for a 500 kV hybrid line

In this paper, the overvoltage distributions due to the lightning stroke are analyzed for a 500 kV hybrid OHTL-Cable-GIL circuit beside substation, in which the section length is variable. Corona effect is incorporating in order to estimate the attenuation and deformation of overvoltage's travelling waves on transmission lines near substations. The influence of connecting substations surge arrester, direct, and indirect lightning strokes are investigated. ATP/Electro Magnetic Transients Program(EMTP) simulation program is applied to analyze the lightning overvoltage of a 500 kV hybrid OHTL-Cable-GIL system. It was discovered that OHTL-Cable, OHTL-GIL, and hybrid systems produces lightning overvoltages higher than those of a fully cable system and very likely lower than those of a fully OHTL system with the same transmission lengths. This means that the risk of experiencing high lightning overvoltages and stressing system components is higher in a fully-Overhead Line (OHL)circuit than in a partial or full cable or GIL line. Furthermore, using the Cable with MOSA (Metal Oxide Surge Arrester), the results have more regular voltage waveform at substation entrance; also Hybrid line has the same effect of fully GIL. Finally, the corona has a less attenuation effect of overvoltage reached to substation by about 2.7% in case short length OHTL.

Lightning protection of a multi-circuit HV-MV overhead line

This paper deals with the assessment of the lightning performance of a medium voltage (MV) power line sharing the same poles of a high voltage (HV) line. We focus on the case of a 15-kV line with compact configuration that is supported by the concrete poles of a 69-kV or a 138-kV transmission line. Due to the taller HV pylons and conductors, the number of direct events to the multi-circuit line is higher than for a MV line alone. The presence of the HV conductors and of the overhead ground wire reduces the amplitudes of the induced overvoltages in the MV conductors due to indirect lightning events. For the considered configurations, with a compact MV line, the number of flashovers per year expected in the double-circuit line due to both direct and indirect flashes is lower than in a MV line alone. It is shown that such a number depends mainly on the line withstand voltage, on the grounding resistance and on the number of surge arresters. The dependence is quantitatively discussed in the paper. The analysis of the overvoltages transferred on the LV side of the distribution transformers is also performed.

Estimation of the expected annual number of flashovers in power distribution lines due to negative and positive lightning

The paper deals with the estimation of the expected annual number of flashovers in overhead power distribution lines due to indirect lightning strokes and aims at extending a procedure previously proposed by the authors, limited to negative downward events, in order to include also positive events. The obtained results show that positive flashes need proper consideration for an improved selection of protection means and countermeasures against flashovers.

Time-Domain PEEC Transient Analysis for a Wire Structure Above the Perfectly Conducting Ground With the Incident Field From a Distant Lightning Channel

This paper presents the time-domain partial element equivalent circuit (PEEC) analysis of induced transients in a wire structure during an indirect lightning strike. The full-wave PEEC formulation with an external incident field is employed. The incident field is calculated with either the Uman's or the Jefimenko's formula by using the engineering model of a lightning channel. An instability problem is, however, observed. It becomes a hurdle in the application of PEEC for evaluating induced transient currents in closed wire loops. The problem is investigated, and is primarily caused by discretization of the electric field in numerical evaluation of external voltage sources. An algorithm is provided to solve this instability problem, and is tested for both near- and far-field cases. It is validated by the finite-difference time-domain method. The issue of time step and segment length is addressed. It is also found that the Uman's formula is generally incapable of producing stable induced currents in a wire loop structure. Finally, the proposed PEEC procedure is applied to evaluate induced lightning transients in a photovoltaic panel during an indirect lightning strike.

Evaluation of Lightning Protection Efficacy on Nigerian Installations High Voltage Installations Using Screen and Cone of Protection Methods

This study evaluated lightning protective system efficacy on 11kV-132kV substation-power line installation in Ikorodu, Lagos State, Nigeria with reference to cloud to ground(C-G) lightning strike (LS) events. It focus on interception of lightning strikes and its protection with reference to direct lightning strike (DLS) and indirect lightning strike (IDLS). Data were collected from Ikorodu 132/33 kV Transmission Substation and its four major injection stations. This work was carried out using physical measurement of raw data obtained from the high voltage substation. Installations were scaled down and modelled dimensionally using AutoCAD software in order to measure spatial parameters in order to measure the screening of the existing substations and connected lines, as well as the existing cone angles of protection. Probability of lightning efficiency of lightning protective level (LPL) are used for screening evaluation while spike and sky wire angle of protection are used for cone of protection evaluation. Physical measurement of six substations (33/11 kV and 132/33 kV substations) in the studied area were also carried out to evaluate the effectiveness of the installed lightning arresters with respect to the protected devices using applicable standard. The results under the prevailing lightning protective system, LPS, (screening method), revealed that the existing 33/11 kV and 132/33 kV substations are not adequately protected against lightning strike; 132/33 kV substation is more vulnerable to lightning strike than 33/11kV substation and that the incoming 132kV power lines to the substation are adequately protected. The evaluation of the installed distances of all lightning arresters are within standard range and would adequately protect substation transformers against travelling waves (Indirect Stroke) events. The installed lightning arresters (LAs) would adequately protect substation transformers against travelling waves (Indirect Stroke) events. The adequate protection should be reinforced with proposed design scheme in further study in order to mitigate the disastrous effects of lightning strike. Any proposed design of protective system for electric power installations in Nigeria should be simulated using computer aided design software for scaled validation of dimensional and spatial design values in order to mitigate reported failures and uncertainties in identifying causes of observed failures in the system.

Evaluation of Lightning Protection Efficacy on Nigerian Installations High Voltage Installations Using Screen and Cone of Protection Methods

This study evaluated lightning protective system efficacy on 11kV-132kV substation-power line installation in Ikorodu, Lagos State, Nigeria with reference to cloud to ground(C-G) lightning strike (LS) events. It focus on interception of lightning strikes and its protection with reference to direct lightning strike (DLS) and indirect lightning strike (IDLS). Data were collected from Ikorodu 132/33 kV Transmission Substation and its four major injection stations. This work was carried out using physical measurement of raw data obtained from the high voltage substation. Installations were scaled down and modelled dimensionally using AutoCAD software in order to measure spatial parameters in order to measure the screening of the existing substations and connected lines, as well as the existing cone angles of protection. Probability of lightning efficiency of lightning protective level (LPL) are used for screening evaluation while spike and sky wire angle of protection are used for cone of protection evaluation. Physical measurement of six substations (33/11 kV and 132/33 kV substations) in the studied area were also carried out to evaluate the effectiveness of the installed lightning arresters with respect to the protected devices using applicable standard. The results under the prevailing lightning protective system, LPS, (screening method), revealed that the existing 33/11 kV and 132/33 kV substations are not adequately protected against lightning strike; 132/33 kV substation is more vulnerable to lightning strike than 33/11kV substation and that the incoming 132kV power lines to the substation are adequately protected. The evaluation of the installed distances of all lightning arresters are within standard range and would adequately protect substation transformers against travelling waves (Indirect Stroke) events. The installed lightning arresters (LAs) would adequately protect substation transformers against travelling waves (Indirect Stroke) events. The adequate protection should be reinforced with proposed design scheme in further study in order to mitigate the disastrous effects of lightning strike. Any proposed design of protective system for electric power installations in Nigeria should be simulated using computer aided design software for scaled validation of dimensional and spatial design values in order to mitigate reported failures and uncertainties in identifying causes of observed failures in the system.