Ground Flash Density Research Articles

Recurrent Lightning Spots: Where Lightning Strikes More Than Twice

AbstractThe expression “lightning never strikes twice” is questioned in this paper because, among the randomness of lightning impacts, some spots are hit even more than twice year after year. This article introduces the recurrent lightning spots (RLS) concept, which are locations periodically impacted by cloud‐to‐ground lightning every consecutive year over a certain period. RLS are investigated in two regimes, with markedly different lightning climatology but similar orography, for 10 consecutive years: Catalonia (North East of Spain, Europe) and Barrancabermeja (North Central Colombia, South America). Results revealed 148 and 916 RLS in Catalonia and Barrancabermeja, respectively. RLS in both regions are typically found to be related to tall structures, mountain peaks, and steep terrain. The method allowed us to identify those tall towers and orographic relief frequently affected by lightning that are not detected with the mere computation of the ground flash density. In the case of Catalonia, some RLS are found offshore. Besides the scientific interest in understanding lightning, the new concept of RLS provides additional and valuable information applicable to lightning protection engineering.

Development of GIS-based Ground Flash Density and its Statistical Analysis for Lightning Performance Evaluation of Transmission Lines in Peninsular Malaysia

Malaysia is one of the world's highest lightning regions, making it an ideal location for studying lightning activities, as they cause many power outages on overhead transmission lines. This study presents ground flash density (GFD) mapping and statistical analysis of lightning flash data in Peninsular Malaysia, which will be used to evaluate the lightning performance of transmission lines. Using Geographical Information System (GIS) software, the GFD map and lightning flash data for statistical analysis were extracted. MATLAB was then used to perform statistical analysis and obtain the probability of peak lightning current using the generalized extreme value (GEV) distribution. This study analyzed six years of lightning flash data from 2012 to 2017 recorded by the Lightning Location System (LLS) and used the Peninsular Malaysia base map from the Department of Survey and Mapping Malaysia (JUPEM). Results show that the GFD mapping approach effectively classifies GFD distribution and identifies areas with high lightning activity. 81% of 4,536,380 lightning flashes were negative polarity, with a higher mean peak current magnitude than positive ones. More lightning activity was observed during the Southwest Monsoon (June-September) and the first Inter-Monsoon season (April-May). Pahang had the most lightning flashes due to its large land area. The GFD map overlaid on the transmission line demonstrated how lightning performance on the transmission line can be assessed. These findings are useful for utility and protection engineers to improve the performance of transmission lines.

Introducing the Concept of the Volume Lightning Strike Density

This letter introduces the concept of the volume lightning strike density (vLSD) and provides the mathematical framework for transitioning from a 2D to a 3D electrogeometric analysis; this may offer new insights into established methodologies for lightning incidence estimation and risk assessment. The feasibility of the vLSD idea is based on the intensive research conducted on emerging technologies of 3D reconstruction of lightning discharges path. Thus, based on the vLSD concept, a new lightning activity parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NV</i> (strikes/km3/yr), that is, the average number of lightning strikes with at least one leader branch per cubic kilometer per year in an area, can be quantified in light of the widespread installation of modern lightning discharge recording systems. This work may open new horizons on lightning activity characterization offering an alternative or complementary approach to the traditional concept of the ground flash density, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NG</i> (flashes/km2/yr); the proposed vLSD concept could also be applied in evaluating the lightning interception efficiency of traditional as well as advanced lightning protection systems especially at critical sites, where enhanced lightning protection is of importance.

OVERVIEW OF FACTORS AFFECTING THE ESTIMATION OF LIGHTNING SHIELDING PERFORMANCE OF OVERHEAD TRANSMISSION LINES

This paper examines the risk of lightning stroke to overhead transmission line. The estimation procedure for the lightning performance of overhead power lines is based on the selected lightning attachment model, available lightning parameter statistics, the transmission tower design and voltage levels, type of overvoltage and other characteristics. In this paper the overview of factors affecting the estimation of lightning shielding performance of overhead transmission lines was performed. Among the factors that can affect the estimation accuracy, one can list insufficiently accurate data on the ground flash density in the area of interest and lack of complete data on statistical distribution of lightning current magnitudes. The paper shows that the influence of wind on the increase in the horizontal exposed distance of the phase conductor is not also taken into account. In this research traditional electro-geometric model was used for estimation of lightning performance of 220 kV overhead power line. Results obtained suggest that swing of suspension insulator strings caused by strong winds may lead to increased risk of lightning shielding failure during thunderstorm. Calculation performed for 3 kA lightning current magnitude shows that at swing angle equal to –1 degree, the horizontal unprotected distance of phase conductor increases by 3.1%, that corresponds to 5.240 m uncovered width. When the swing angle is increased to –5 degree, the uncovered width is increased by 15.8% that corresponds to 5.885 m uncovered width. It is proposed that an increase in the risk of lightning shielding failure as a result of wind load can be accounted by applying an appropriate correction factor in expressions for calculation of shielding failure rate, shielding failure flashover rate, etc. Proposed correction factor should account frequency and strength of wind in the area of transmission line route and depend on transmission line voltage level and tower design. Further efforts should be focused on obtaining and justifying the numerical values ​​of this correction factor.

The Impact of Direct Lightning Strike Damages on PV Modules in a Large Malaysian PV Farm

Many lightning risk analyses avoided considering the role of the PV Module’s aluminium frame as a natural lightning air termination system or if such a role is considered, assumed that the ‘thin’ aluminium frame, would not be damaged from metal melting and evaporation at the point of lightning stroke attachment. Although the IEC 62305 is not lacking in guidance on the use of thin metal sheets as air terminations, this aspect is not considered in PV farm design. To ensure correct inputs into the risk assessment calculation, the evaluation of interception and sizing efficiencies and the damage probabilities of the natural components have to be addressed. A comparative analysis is done between two types of air terminations; the PV-frame LPS and the finial-added LPS. The result indicates that for solar PV farms exceeding a certain size and operating in high ground flash density regions like Malaysia, the finial air termination may out-perform the PV-frame LPS.

ANALYSIS OF APPROACHES FOR ESTIMATING THE LIGHTNING PERFORMANCE OF OVERHEAD TRANSMISSION LINES

Purpose. A review of the current literature, regarding the existing approaches used to estimate the lightning perfor-mance of overhead power lines, was performed. A review of available lightning activity data over India was also per-formed. Methodology. The electro-geometrical model was chosen to analyze the lightning performance of overhead power lines. International normative documents and national standard were used to highlight the main parameters that should to be paid main attention to when estimating lightning performance of overhead power lines. Results. Presently, approaches from IEEE and CIGRE guides can be used for analysis of statistical distributions of lightning current pa-rameters. Further studies are required on thunderstorm days, ground flash density and current parameters statistical dis-tributions for different locations, which will be supportive in performing analysis for Indian power lines. Originality. To graphically analyze the shielding failure mechanism with a help of electro-geometric model, the sketch of real 220 kV double-circuit transmission line tower was used. Using electro-geometric model it was graphically shown how downward lightning leader that propagate from thunderstorm cloud toward ground can finish its path on the overhead shield wire, phase conductor or ground plane. Practical value. Available data on lightning activity over different parts of India are still not enough complete. It is of great importance to obtain reliable statistical data on thunderstorm characteristics in the area of the studied power line route. Measurement techniques based on satellites have limitations in obtaining ground flash density values. Thus, for India there is a need in development of modern lightning detection networks and related studies on lightning characteristics. Conclusions. Future efforts should be focused on obtaining not only the positions and number of lightning strikes to the overhead power line, and calculation of lightning flashover rate parameters, but also the statistical distributions of lightning current values and related overvoltage parameters at the overhead wires and different phase conductors. References 21, figures 4.

Analysis on Management Strategy of Lightning Protection in Hunan Distribution Lines

The lightning activity is frequent in Hunan, and frequent lightning activities seriously affect the safe and stable operation of distribution network equipment. The statistical analysis of lightning trip-out in Hunan distribution line is made in this paper. According to the current situation of lightning protection in Hunan distribution lines, the differentiated lightning protection management strategy is proposed, which takes into account the ground flash density and special landform factors. And the field application in the past year shows that the effect of lightning protection is good. However, there are also corresponding management and technical problems in the implementation process. The corresponding solution ideas and suggestions are put forward in this paper based on the fully investigation and the experimentation simulation, which has the certain reference value for further improving the lightning withstand level of hunan distribution lines.

A Methodology for Protection of Trees Against Lightning Strikes as a Measure to Prevent Fires and Loss of Human Life

Some regions may be characterized by a very low annual lightning ground flash density, and yet lightning strikes seem to have been in those areas the cause of widespread wildfires in forested areas. Due to global climate change, these occurrences seem to be an increasing threat. In this article, the authors discuss the withstand capability of trees against lightning and introduce the criteria for the deployment of tree lightning protection systems to protect forested areas, where deemed necessary by the tree risk assessment. This work analytically identifies the critical trunk radius of the tree below which the tree may explode in the case of a lightning strike and ignite the surrounding vegetation. The critical heights of trees requiring lightning protection systems to prevent loss of human life and cultural heritage are also identified.

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.

The Variation of Lightning Current Parameters with Altitude in Shandong Region

Lightning current parameters is the basis of the transmission line design and transformation essential parameters of lightning location system somewhere in shandong area ground ground lightning information lack of height of the statistical properties, not situation, the analysis of the influence of altitude on lightning parameters using global digital elevation data filled in the lightning location data in the lack of information, analysis of the lightning current parameters and the relationship between the altitude in the region. The variation of lightning current amplitude, lightning return times, ground flash density and other factors with altitude is studied, and the variation law of lightning parameters in this area with altitude is obtained. When the altitude is 1200∼2000m and 2400∼3200m, the number of lightning return stroke fluctuates greatly. When the altitude is from 2000 to 2800m, the number of lightning return strokes increases with the increase of altitude. With the rise of altitude, the proportion of normal lightning flashes in total lightning flashes in shandong area has a tendency to increase gradually. Due to the shortcomings of the above three kinds of observation data, we try to learn from each other to better reflect the lightning activity rule in shandong more comprehensively, accurately and effectively, and to provide certain theoretical basis and help for lightning protection and disaster reduction work, providing reference for the design and lightning protection transformation of power grid in shandong.

Sensitivity analysis of lightning stroke-to-flash grouping criteria

Lightning Location Systems provide detailed data on the lightning occurring within the area of the system's coverage. This kind of remote sensing equipment uses geolocation techniques to retrieve lightning cloud-to-ground return strokes. Prior to getting information regarding the number of lightning flashes, cloud-to-ground strokes need to be grouped into lightning flashes. The stroke-to-flash conversion is not straight forward and therefore, a stroke-to-flash grouping criteria (flash algorithm) is needed to obtain subsequent figures like the Ground Flash Density (NG). It is now more than twenty years since the most used stroke-to-flash grouping criteria was established: 1 s, 10 km radius and 500 ms inter-stroke interval.In the course of these years, new observational systems like the Lightning Mapping Array have been deployed to precisely depict the lightning flash extension and duration. The present work aims to introduce a new approach to the flash algorithm, taking advantage of the Lightning Mapping Array capabilities. Two methods based on this system have been used in this study as an alternative way for grouping cloud-to-ground strokes into flashes. These methods are compared with the classical flash algorithm. Results suggest shortening the total flash duration and enlarging the clustering radius. Besides, this work also analyses the sensitivity of the flash algorithm to the changes on the grouping criteria. Changes in these parameters will have a bearing on the retrieved annual number of lightning flashes, and thus will also influence derived lightning figures like the NG.

Monte‐Carlo‐based simulation and investigation of 230 kV transmission lines outage due to lightning

Here, using the probabilistic evaluation based on the Monte Carlo method, back-flashover rate and shielding failure flashover rate of 230 kV overhead transmission lines in the western regions of Iran are evaluated. To such an aim, first, the number of thunderstorm days per year is collected from the reported weather information in order to determine the ground flash density. Then, using MRU-200 equipment, the tower-footing resistance of several towers is measured. Matlab® software is used in order to produce lightning surges considering its probabilistic nature and randomly distribution on the ground to evaluate striking distance based on the geometric model. Then, calculated parameters are transferred to EMTP-RV software by establishing a link to perform the transient simulation and report the results for modelled 230 kV transmission line. Finally, considering IEEE-1243 standard, it is shown that due to high ground flash density, using 230 kV tower with one shield wire is not sufficient to protect the line against lightning phenomena.

GENETIC ALGORITHM BASED LIGHTNING ESTIMATION MODEL

When lightning strikes to the transmission line, orifices in the insulation can be created. As a result, the insulation co-ordination between phases is breakdown and over-voltage will propagate across the transmission line in the form of electrical fields. Hence, the system will encounter under-frequency and prolonged type of destruction. In a worst-case situation, it may lead blackout. One of the effective ways to reduce lightning impact is to identify the lightning activity. This researchhas been carried out to familiarize the lightning activity in Sarawakarea;hence, the Genetic Algorithm (GA) is utilized to optimize the crucial constants of the lightning empirical equation. As the constant values are successful to be optimized, estimation of Ground Flash Density (GFD) can be performed. The performance is evaluated using Matlab. Using the GA optimized parameter the estimations areprecise. To achieve estimation that is more accurate many trials are required to be carried out in order to determine the best fitness value. In this article, three casesare carried out in determining the optimal solution in term of constant “a” and “b” for each sub-region in Sarawak.

Cloud-to-ground lightning flash density and the number of lightning flashes hitting wind turbines in Japan

The current status of the Japanese coastal region shows that winter lightning has seriously damaged wind turbines owing to its larger electrical charge than summer lightning. In Japan, 64% of serious wind turbine damage occurred in winter. Typically, lightning flash density is used to evaluate lightning risk in an area. Herein, we discuss the extent of lightning damage on wind turbines in Japan and cloud-to-ground (CG) lightning flash density based on the Japanese Lightning Detection Network, the largest lightning location system in Japan. Consequently, we found no correlation between the number of lightning flashes hitting wind turbines and summer lightning ground flash densities in the surrounding areas of a wind turbine. Approximately 95% of the lightning flashes that hit the turbine occurred in winter. The probabilities of lightning flashes hitting wind turbines were 0.12% in summer and 5.6% in winter. We developed a map showing the probability of lightning flashes hitting wind turbines in Japan. The probabilities obtained using this map were quite similar to the CG lightning flash density in winter. Therefore, we propose that lightning risk for wind turbines should not be evaluated based on the annual CG lightning flash density in Japan.

Transient modeling of the wind farms in order to analysis the lightning related overvoltages

Abstract During transient analysis of lightning surge, the distributed stray capacitances on wind turbine structure and the grounding system of tower have a considerable effect on the generated overvoltagese that must be included in the calculation. Therefore, the accurate modeling of wind farms is vital. This paper presents the wide-band modeling of the wind farm so that different parts of the structure and frequency-dependent behavior of the grounding system are modeled. Also, a case study is implemented in the EMTP-RV in order to analyze the effects of the proposed method on the calculated overvoltages. The results show that the wide-band modeling of the wind farms results in the lower estimation of the overvoltages than to the previous methods with the difference that is more pronounced in the soil of high resistivity. Among different components of the structure, the proposed model has the most effect on the estimation of the ground potential. Furthermore, the arrester lifetime estimated by the proposed method is bigger than to the previous methods, in which the difference decreases with the ground flash density increasing. The presented method would be beneficial when designing lightning protection scheme and select optimal rating of the arresters for the intended wind farms.

Kosovo’s Ground Flash Density and Protection of Transmission Lines of the Kosovo Power System from Atmospheric Discharges

In this paper is presented the protection of transmission power lines of the Kosovo Power System from atmospheric discharges, with the use of surge arresters. Atmospheric discharges represent one of the main causes of interruptions for the Kosovo Power System. In addition, the ground flash density for Kosovo is given. The transmission lines with the worst performance regarding atmospheric discharges are discussed in more detail and are presented recommendations about the surge arresters used to protect the system from these overvoltages. The data provided by the localized lightning system in Kosovo enable us to provide a detailed correlation of the reported outages of the Kosovo Power System and corresponding atmospheric discharges. Recommendations for protection in terms of surge arresters are given followed by subsequent dynamic simulations using MATLAB software.

Cloud-to-ground lightning activity in Colombia and the influence of topography

Lightning activity on the Colombian mountains, where the altitude varies from 0 to more than 5000MSL, is studied based on VLF/LF lightning detection data and using a 2012–2013 dataset. The influence of altitude is observed by evaluating cloud-to-ground lightning incidence at different altitude intervals. The relationship between ground flash density and altitude gradient vectors is studied. Results show a clear dependence of the flash density on elevation.

Lightning severity in Malaysia and some parameters of interest for engineering applications

To the electric utility engineer, the parameters of the flash that are of primary interest are the crest current for the first and subsequent strokes, the waveshape of these currents, correlation between the parameters, the number of strokes per flash and flash incidence rates where the ground flash density, denoted as flashes per square km-year and symbolized by Ng. The first three parameters, as we know them today, are to a very large extent based on the measurements of Berger. Berger's masts, 70 and 80 meters high, were mounted atop Mt. San Salvatore (Switzerland), which is 650 meters above Lake Lugano, where it can be readily noted that these 125 records represent one of the best and most extensive set of data available to the industry to date. This paper focuses on the lightning severity scenario in Malaysia, which could also applicable to other tropic countries, and some of the useful parameters for lightning protection system design and forensic study. Some specific engineering applications have also been summarised, taking into account various lightning parameters, available from past and current measurements available.

Contribution to Lightning Parameters Study Based on Some American Tropical Regions Observations

This paper presents a recent characterization review of three cloud-to-ground lightning parameters [lightning peak current, ground flash density, and keraunic level (KL)] used in engineering applications based on available data from studies conducted in some tropical countries of Central and South America (Brazil, Colombia, Costa Rica, and Venezuela), considering seasonal and spatial variation aspects. There are some differences between the behaviors of the analyzed parameters in tropical areas in comparison with those published in the literature for temperate ones. The most significant conclusion is that historical data suggest that the highest ground flash density are located between latitude of 8° and 10° north. This value is much higher than the highest values reported for countries located in temperate regions. It is seen from the KL analysis that this parameter varies depending on the latitude with values up to 200 thunderstorm days (TDs).

Spatial and temporal variations of thunderstorm activities over Sri Lanka

Spatial and temporal variation of frequencies of thunderstorms over Sri Lanka using thunder day data is presented. A thunder day is simply a calendar day in which thunder is heard at least once at a given location. Two sets of data were collected and analyzed: annual totals for 10 climatological stations for a period of 50 years and monthly totals for 20 climatological stations for a period of 20 years. The average annual thunder days over Sri Lanka was found to be 76. Among the climatological stations considered, a high number of annual thunder days was recorded in Ratnapura (150 days/year), followed by Colombo (108 days/year) and Bandarawela (106 days/year). It appears that there are no widespread long-term increasing or decreasing trends in thunderstorm frequencies. However, Colombo, the capital of Sri Lanka which has over two million people shows an increasing trend of 0.8 thunder days per year. Although there is a high variability between stations reporting the number of thunder days, the overall pattern within a year is clear. Thunderstorm frequencies are high during two periods: March–May and September–November, which coincide with the first inter-monsoon and second inter-monsoon periods. Compared to the dry zone, the wet zone, especially the southwestern region, has high thunderstorm activity. There is a clear spatial difference in thunderstorm activities during the southwest and northeast monsoon seasons. During both these seasons, enhanced thunderstorm activities are reported on the leeward side of the mountain range. A slight reduction in the thunderstorm activities was found in the high elevation areas of the hill country compared to the surrounding areas. A lightning ground flash density map derived using annual thunder days is also presented.