Lightning Attachment Models Research Articles

Evaluation of the backflashover performance of 150 kV and 400 kV double-circuit overhead transmission lines as affected by lightning attachment models and peak current distributions

The evaluation of the backflashover performance of overhead transmission lines requires the adoption of a lightning attachment model and a peak current distribution. These affect the estimated backflashover rate, BFR, of the lines. The present study aims to quantify the influence of lightning attachment model and peak current distribution on the BFR of double-circuit overhead lines. This is achieved by evaluating typical 150 kV and 400 kV lines. ATP-EMTP simulations are conducted to obtain the critical currents causing backflashover of line insulation. Then, the critical currents are used in lightning incidence computations to obtain BFR. The influencing parameters taken into account in this work are the low current and low frequency tower ground resistance, the location of lightning strike to the shield wire along the span, and the AC voltage phase angle, all affecting the critical backflashover current. Several lightning attachment models and peak current distributions are evaluated. Their influence on BFR is found to be considerable, especially for lower tower ground resistance values. The lightning peak current distributions yield more pronounced effects on BFR. The results of this study stress the need for computing BFR using a more accurate expression than the simplified one based on CIGRE TB 63.

Evaluating protection against lightning for historical buildings and cultural heritage monuments

A review on the lightning risk management and lightning protection of historical buildings and cultural heritage monuments is presented. Cases of lightning-related damages to historical monuments worldwide are presented with emphasis given to cases in Greece. Recorded incidents stress the need for an effective lightning protection system (LPS) design, ensuring sufficient protection of the monument against lightning, including its installations and contents, as well as persons. External LPS of several monuments and historical buildings worldwide are also presented. An external LPS has been designed for the Parthenon monument in Greece in accordance with IEC 62305. The LPS design has been evaluated based on a stochastic lightning attachment model. Revisions to the risk management of IEC 62305 with special focus on historical buildings and cultural heritage monuments are suggested. As this special category of structures is most commonly subject to constraints with respect to aesthetic intervention and construction, dedicated studies employing alternative methods for LPS design, based however on physical grounds, are required.

Research on the Initiation of Multiple Upward Leaders From an Isolated Building Based on an Improved Lightning Attachment Model

AbstractMore and more optical records have exhibited that multiple upward leaders (MULs) occur frequently on a building in the flash attachment process. An interesting issue is why a building can continue to launch upward leader (UL) after the first one appears. This phenomenon is analyzed in the present paper. Considering the influence of the leader behaviors on the ambient electric field, an improved 3‐D fine‐resolution lightning attachment model with MULs is established to simulate cloud‐to‐ground flash events with diverse leader spatial morphologies. The simulation results show that MULs may initiate almost simultaneously or with an obvious delay and the variation range of UL length is large. From this, the flash events of lightning terminating on a building are divided into four scenarios and each scenario is analyzed. It was found that the spatial location of downward leader, the length and propagation direction of the first UL and the time interval from the inception of the first UL to final jump significantly affect the electric fields at top corners of building and further affect the inception of the second UL. Based on qualitative analysis, four factors are proposed to explain why the above four scenarios happen.

Estimating the shielding failure flashover rate of single-circuit overhead lines with horizontal phase configuration via stochastic lightning attachment simulations

A methodology is proposed for estimating the shielding failure flashover rate (SFFOR) of single-circuit overhead lines with horizontal phase configuration. An application to a 66 kV overhead line is presented. A stochastic lightning attachment model is employed, based on the concept of fractal structures, to compute the probability of shielding failure to the line. Results of stochastic modeling are combined with those of an ATP-EMTP model for estimating the critical lightning currents causing flashover of the line insulation. Shielding failure results of the proposed methodology are compared and discussed with results obtained employing the methodology of the IEEE Std 1243. Innovation of this work lies in estimating the SFFOR of overhead lines by considering the stochastic nature of lightning attachment, physical criteria associated with leader discharges’ inception and propagation, as well as electromagnetic transient simulations to predict lightning-related flashover to overhead lines accurately.

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.

A Fractal-Based Approach to Lightning Protection of Historical Buildings and Monuments: The Parthenon Case Study

A fractal-based approach to the lightning protection of historical buildings and monuments against direct lightning flashes is introduced. The proposed methodology is based on a stochastic lightning attachment model that considers physical criteria on downward and upward leaders’ inception and propagation. The model foresees multiple competing upward leaders incepting from vulnerable points of the monument under protection and considers the branching and tortuous behavior of the lightning attachment phenomenon. Applying the proposed methodology to the Parthenon has shown that the risk of direct lightning flashes per year that cause physical damage to the monument is not acceptable without an external lightning protection system (LPS); two different LPSs are evaluated in terms of lightning interception efficiency. Lightning risk assessment results are discussed and compared with those obtained by implementing the procedures of the International Electrotechnical Commission (IEC) 62305.

ICCD Images of Leader Corona in a 4 m Rod-Plane Gap Discharge

As the featured discharge pattern and widely present in lightning discharge channels, leader corona system is crucial for continuous leader propagations in long air gap discharges and natural lightning, which had attracted numerous studies experimentally or theoretically. In the simulation of discharge process and lightning attachment calculations, the vertex angle of streamer zone ahead of leader channel is the crucial parameter, which could only be obtained by discharge experiments. As a result, morphological researches on leader corona system gave an intuitive insight on the streamer zone ahead of the leader channel and helped comprehensive theoretical modeling studies especially in the calculation of electric field. In order to obtain the accurate shape features and provide the calculation parameter for model modification, in this paper, experiments of 4-m long air gap discharges were carried out based on a four-frame PCO.dicam C4 ICCD camera. Clear images of leader corona were observed. Results showed that the corona zone was assumed as conical and the average angle at the vertex was 75.2° which was less than the first corona during the stable leader propagation stage. Influences of exposure time and leader branching phenomenon were investigated in this paper. It was concluded that the competitive relationship of the branched leaders shrank the vertex angle of the conical corona zone. Results in this paper could instruct the future theoretical model researches on leader corona system and help to modify the existing lightning attachment models like SLIM or leader process model.

A Stochastic Model for Evaluating the Lightning Performance of a −400 kV HVDC Overhead Line

A stochastic lightning attachment model for evaluating the lightning performance of overhead transmission lines is introduced. The proposed model considers the stochastic nature of lightning attachment by taking into account the lightning discharge branched and tortuous behavior. It integrates physical criteria on leader inception by adopting the Petrov and Waters model, as well as leader discharge progression considering also the competing interaction of multiple upward leaders. A generalized methodology combining stochastic modeling of lightning incidence with an electromagnetic transients (EMT) simulation model is proposed so as to estimate the backflashover and shielding failure flashover rates of HVDC overhead lines; an application to a monopolar −400 kV line sheds light on the basic parameters that affect the lightning performance of HVDC lines. The probability of shielding failure is higher than that obtained by the deterministic lightning attachment models. The stochastic nature of lightning attachment and the effect of lightning peak current distribution should be considered for the design and evaluation of the lightning performance of the emerging HVDC systems.

Estimation of Lightning Incidence to Telecommunication Towers

General closed-form expressions for estimating lightning incidence to telecommunication towers are introduced on the basis of several lightning attachment models. The expressions consider the effects of tower height and lightning peak current distribution, as well as orographic and shielding effects. The estimated annual number of lightning strikes to towers, varying considerably among lightning attachment models, increases with tower height according to a power law and it is higher for lightning peak current distributions with high median value and standard deviation. A comparison is made between estimates and field data on lightning incidence; IEC geometric method, which is traditionally used in industry, by exaggerating the effect of tower height, overestimates lightning incidence. Literature lightning attachment models suitable for estimating lightning incidence to telecommunication towers are suggested based also on the observed failure rate of a transformer feeding a GSM base station.

Lightning Shielding Analysis on Ships

Calculations of the expected number of lightning strikes on three ship models are presented with comparative application of various lightning attachment models and stroke current distributions. Depending on the ship structure, on coastal areas, a lightning strike on a ship is expected approximately every two years. Application of the rolling sphere method highlighted as regions exposed to lightning strikes not only high masts but also lower structures in the cases of ships with less dense geometry. A new method for the lightning protection of critical masts that combines a shielding analysis procedure and a statistical lightning interception model was also proposed and applied to specific masts of the ship models in order to evaluate whether shielding from nearby higher masts is achieved and to define the proper height and installation position of a new rod. Proximity effects, interception probability, and choice of the ground reference level arise as parameters that affect the results of the shielding analysis, especially when the equipment under protection is the highest structure on the ship.

Lightning attachment process to common buildings

AbstractThe physical mechanism of lightning attachment to grounded structures is one of the most important issues in lightning physics research, and it is the basis for the design of the lightning protection systems. Most of what is known about the attachment process comes from leader propagation models that are mostly based on laboratory observations of long electrical discharges or from observations of lightning attachment to tall structures. In this paper we use high‐speed videos to analyze the attachment process of downward lightning flashes to an ordinary residential building. For the first time, we present characteristics of the attachment process to common structures that are present in almost every city (in this case, two buildings under 60 m in São Paulo City, Brazil). Parameters like striking distance and connecting leaders speed, largely used in lightning attachment models and in lightning protection standards, are revealed in this work.

On the possible variation of the lightning striking distance as assumed in the IEC lightning protection standard as a function of structure height

The effect of structure height on the lightning striking distance is estimated using a lightning strike model that takes into account the effect of connecting leaders. According to the results, the lightning striking distance may differ significantly from the values assumed in the IEC standard for structure heights beyond 30m. However, for structure heights smaller than about 30m, the results show that the values assumed by IEC do not differ significantly from the predictions based on a lightning attachment model taking into account the effect of connecting leaders. However, since IEC assumes a smaller striking distance than the ones predicted by the adopted model one can conclude that the safety is not compromised in adhering to the IEC standard. Results obtained from the model are also compared with Collection Volume Method (CVM) and other commonly used lightning attachment models available in the literature. The results show that in the case of CVM the calculated attractive distances are much larger than the ones obtained using the physically based lightning attachment models. This indicates the possibility of compromising the lightning protection procedures when using CVM.

Statistical method for the evaluation of the lightning performance of overhead distribution lines

Lightning is a major cause of distribution line outages affecting reliability of power supply thus, consequently, resulting in economic losses. The lightning performance of overhead distribution lines is associated with line insulation flashover due to direct and nearby lightning strokes. The present paper introduces a statistical method for the estimation of the flashover rate of overhead distribution lines. The proposed method, implementing a recently introduced statistical lightning attachment model and the simplified coupling model suggested by the IEEE Std. 1410:2011, yields a range for the expected flashover rate of distribution lines associated with lightning interception probability distribution of the line conductors. It also provides the means to easily quantify the effects of line parameters, soil resistivity, shielding of nearby objects and lightning crest current distribution on lightning performance of distribution lines. Results of the statistical method, discussed and compared with that obtained by the IEEE Std. 1410:2011, are in close consistency with field data.

Estimation of the shielding performance of overhead transmission lines: The effects of lightning attachment model and lightning crest current distribution

Shielding failure of overhead transmission lines is a major cause of transmission system outages, affecting reliability of power supply and resulting in economic losses. In this study the shielding performance of overhead transmission lines is evaluated with the aid of general expressions, derived by implementing in shielding analysis different categories of lightning attachment models. Thus, the effects of lightning attachment model, transmission line parameters and lightning crest current distribution on shielding failure rate of overhead transmission lines have been quantified. Alternative approaches to that proposed by IEEE Std 1243 for assessing the shielding performance of transmission lines, including computer simulations of lightning attachment, are evaluated. Shielding failure rate results are discussed and compared with field data reported in literature. For typical overhead transmission lines, an upper limit of the estimated shielding failure rate is 0.4% of the rate of lightning strokes to the line. More and reliable field data is needed in order to evaluate lightning attachment models with respect to the lightning performance of overhead transmission lines.

Lightning attachment models and maximum shielding failure current of overhead transmission lines: implications in insulation coordination of substations

The maximum shielding failure current of overhead transmission lines is an important parameter in evaluating the shielding performance of the lines and in insulation coordination of substations. General expressions for the estimation of the maximum shielding failure current of transmission lines, derived by employing several lightning attachment models in shielding analysis, are presented. An application to typical 110 kV up to 1150 kV overhead transmission lines shows that there is a great variability in maximum shielding failure current among lightning attachment models. The importance of maximum shielding failure current in insulation coordination of substations is demonstrated with the aid of alternative transients program-electromagnetic transients program (ATP-EMTP) simulations. The computed overvoltages impinging on 150 and 400 kV gas insulated system (GIS) substations because of shielding failure of the incoming overhead transmission lines, being dependent upon shielding failure current, vary with the lightning attachment model employed in shielding analysis of the lines. Implementation of the electrogeometric model adopted by IEEE Std 1243:1997 in shielding analysis imposes high requirements on protection of the substations against incoming shielding failure surges.

Estimation of Lightning Incidence to Overhead Transmission Lines

General expressions for the estimation of lightning incidence to overhead transmission lines on the basis of electrogeometric and generic models are introduced, which consider, besides transmission-line geometry, lightning crest current distribution and, based on the recently proposed statistical model, interception probability distribution. An application to typical 115 kV up to 765 kV and large scale 500 kV and UHV overhead transmission lines is performed and the computed results, varying significantly among lightning attachment models, are validated through comparisons with field data from literature; the IEEE Std 1243 overestimates significantly lightning incidence to shield wires of large scale transmission lines. The expected annual number of lightning strikes to shield wires of transmission lines depends on lightning crest current distribution; this dependence, easily quantified with the aid of the introduced general expressions, is not considered by the relevant IEEE standard. Lightning incidence results are discussed in the context of the backflashover rate of overhead transmission lines.

‘The mesh method’ in lightning protection standards – Revisited

At present the design of the Lightning protection systems (LPS) for structures as stipulated in standards is based on the electro – geometrical method, which was initially used to protect power lines from lightning. A derivative of the electro-geometrical method is the rolling sphere method. This method together, with the protection angle method and mesh method are used almost in all lightning standards as the measure in installing the lightning protection systems of grounded structures. In the mesh method, the dimension of the cell size in different levels of protection is determined using the rolling sphere method. Since the rolling sphere method does not take into account the physics of the lightning attachment process there is a need to evaluate the validity of the stipulated value in standards of the minimum lightning current that can penetrate through the mesh in different levels of protection. In this paper, meshes of different sizes as stipulated in the lightning protection standards were tested for their ability to intercept lightning flashes using a lightning attachment model that takes into account the physics of connecting leaders on. The results are in reasonable agreement with the specifications given in the lightning protection standards.