Assessment Of Lightning Performance Research Articles

Influence of a shield wire flashover on the indirect lightning performance assessment of distribution lines

This paper presents a new aspect of shield wire (SW) modeling for assessing the indirect lightning performance of overhead medium-voltage distribution lines: a flashover (FO) between an SW and the reinforcing bars of a distribution pole or a crossarm (SWFO). In general, an SW is periodically grounded approximately every four to ten poles and not grounded at the other poles. However, owing to lightning-induced overvoltages, the voltage difference between the SW and the distribution pole may even exceed 100 kV, and the SWFO can occur. In this paper, we evaluate the effect of the SWFO on the number of FO occurrences of phase-conductor insulators by the Monte Carlo method using a 2D finite-difference time-domain-based indirect lightning surge analysis program. The effect of the SWFO is more significant in lines with high soil resistivity (a soil resistivity of 1000 Ωm was assumed) regardless of the installation of surge arresters: the total number of FO occurrences markedly differs by up to 50% between cases in which the SWFO is considered and not considered. The analysis presented in this paper will assist the formulation of lightning protection measures particularly, in regions with high-resistivity soils.

LEMP and ground conductivity impact on the direct lightning performance of a medium-voltage line

• Assessment of the LEMP influence on direct lightning overvoltages of medium-voltage distribution lines of the type equipped with a shield wire and surge arresters. • Comparison between the results obtained by a 3D-FDTD method and the LIOV-EMTP code. • The LEMP contribution on the overvoltages across insulators increases with increasing values of the soil conductivity. • The appropriate modeling of the LEMP effects is important for the lightning performance assessment of the type of lines considered in this paper. In medium-voltage distribution lines equipped with a multi-grounded shield wire and with surge arresters installed along the line at relatively short intervals, lightning outages associated with indirect lightning are less frequent than those associated with direct ones. The protection for this type of distribution lines is therefore dependent on the response to direct strikes. This paper presents and analyses the response to direct lightning overvoltages of lines of such a type located over a lossy soil considering the influence of the lightning electromagnetic pulse (LEMP), which is typically disregarded in the calculation of overvoltages due to direct strikes. The calculation results, performed by means of a three-dimensional finite-difference time domain (3D-FDTD) method and of the LIOV-EMTP code, indicate that the voltage across the insulator is enhanced by LEMP effects. In addition, it is shown that the enhancement due to the LEMP increases with the increase of the soil conductivity value. The modeling of the LEMP effects is therefore important for the accurate assessment of the lightning performance of medium-voltage distribution lines of the type considered in this paper, even when direct strikes are considered.

Estimation of the Lightning Performance of Overhead Lines Accounting for Different Types of Strokes and Multiple Strike Points

Dealing with lightning performance computation, researchers usually consider only negative downward first return strokes and the relevant channel-base peak current distribution. The aim of this article is to account for the lightning flash mechanism, which means to include also downward negative subsequent strokes and downward positive strokes, taking into account available distributions of the number of strokes per flash (i.e., the flash multiplicity) and of the distance among the impact points of the strokes within the same flash (i.e., the channel terminations distance). In this regard, to the best of the authors’ knowledge, the present study is the first one taking into account the multiple ground channel terminations in the lightning performance assessment. The obtained results show that both the negative subsequent strokes and multiple channel termination determine a significant increase in the estimated number of flashovers per year, and they need to be considered in the lightning performance assessment. On the other hand, considering positive downward strokes, a less remarkable increase in the estimated number of flashovers per year is observed.

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.

Lightning Performance Assessment of Power Distribution Lines by Means of Stratified Sampling Monte Carlo Method

This paper proposes the application of a recursive stratified sampling technique for improving the assessment of the lightning performance of power distribution lines through the application of the Monte Carlo method. The accuracy of the results is expressed by means of the confidence interval of the estimated annual number of expected overvoltages. This paper shows the results for a single overhead line, with and without surge arresters, and the case of a feeder with laterals. The adoption of the stratified sampling techniques allows for a computational time reduction up to more than 75% with respect to a standard Monte Carlo procedure. The conceived calculation procedure is applicable to any type of network, regardless of the presence of nonlinear devices and avoiding the application of any heuristic rule.

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.

Application of Local Environmental Data to the Lightning Performance Assessment of the IECo Transmission-Line Network

The paper reports on a second part of the lightning performance study that was conducted on overhead double-circuit lines 170 kV operated by Israel Electric Corporation (IECo). The first part of this study was published this year in TPWRD vol. 31 No. 2 ( [1] ) which introduces the local environmental data including a long-term lightning incidence records, tower footing resistance, and route terrain characteristics. The goal of the present paper is to demonstrate application of the data-inputs from [1] to analysis of the relationship between the line failure rate and its design and environmental parameters. The findings imply that the prevalent lightning failure mechanism in IECo Grid is direct-strike related. The acquired results prove a conclusion on that the ineffective shielding design in combination with local stroke current statistics, route topography, and long spans may seriously compromise line reliability, even with temperate local lightning activity. Disregarding the route terrain specificity may falsify the shielding flashover failure rate assessment and devaluate the line protection design.

LPAT: An interactive simulation tool for assessing the lightning performance of Hellenic high voltage transmission lines

The paper presents the Lightning Performance Assessment Tool (LPAT), an interactive simulation tool which assesses the lightning performance of high voltage transmission lines. The LPAT design was based on a recently published methodology that has been developed in order to assess the lightning performance of the Hellenic high voltage transmission lines. This methodology has been adapted to enable tool's users to enter a large dataset required for the computations eliminating the possibility of mistakes. Moreover, LPAT, written in a high-level programming language and using the appropriate user interface models and programming architecture, enables electrical engineers to adapt the level of granularity in which they prefer to examine the lightning performance of a transmission line. This approach is proved to be ideal for electrical systems such as the Hellenic transmission system whose individual characteristics depend upon the meteorological and geographical characteristics of the Hellenic territory. This tool is also flexible to any modification and change in order to support different transmission systems. The presented simulation tool is valuable for designers of electric power systems intending in a more effective lightning protection.

Lightning performance assessment of Hellenic high voltage transmission lines

A methodology for assessing the lightning performance of Hellenic high voltage transmission lines has been developed. Its main advantage is that the analysed transmission line is divided into regions and the analysis is conducted separately for each one region, taking into account the individual characteristics, which exist in each one of them. The developed approach intends to offer more accuracy in the assessment of lightning performance of Hellenic high voltage transmission lines and of similar lines, where they run at the same time through a plain region, a coastline and/or a mountainous region. The aims of the paper are to describe in detail the proposed methodology and to present results obtained by its application on operating Hellenic transmission lines of 150 and 400 kV. The computed results are compared with the results produced by another software tool published in the technical literature and with the real records of outage rate showing a good agreement. The presented methodology, which is coded in a comprehensive computer program, can be proved valuable to the studies of electric power systems designers intending in a more effective lightning protection.

An Improved Procedure for the Assessment of Overhead Line Indirect Lightning Performance and Its Comparison with the IEEE Std. 1410 Method

This paper deals with the assessment of the lightning performance of distribution lines, namely the estimation of the annual number of lightning-induced flashovers versus the critical flashover voltage of the line insulators. The procedure proposed by the authors is compared with the one described in IEEE Std. 1410-2004 Guide for improving the lightning performance of electric power overhead distribution lines. The two methods differ: 1) for the models adopted to evaluate the induced voltages and 2) for the adopted statistical approach. The reasons for differences in the results predicted by the two methods are discussed and the parameters playing the major role in the achievement of the results are identified. The proposed method represents an improvement compared to IEEE Std. 1410 because it takes into account more realistic line configurations and the effect of the finite ground conductivity

Effect of tall instrumented towers on the statistical distributions of lightning current parameters and its influence on the power system lightning performance assessment

AbstractStatistical distributions of lightning current amplitude, time‐to‐peak and other lightning current parameters used in power system insulation coordination are based on experimental data obtained by means of tall instrumented towers. It is, however, generally accepted that these distributions, which we will call ‘classical’ ones, are affected by the presence of the tower, as the tower ability to attract lightning flashes tends to increase for flashes with larger currents. Current amplitudes are thus biased towards higher values with respect to those which refer to flashes at ground. In this paper, we adopt a procedure recently proposed by the authors to infer the statistical distributions of lightning current parameters at ground level starting from those obtained from data measured using tall instrumented towers. The procedure is first applied to classical statistical distributions of lightning current parameters to quantify the tower bias, and this for various models that have been proposed in the literature to represent the exposure of the tower to direct strokes. Then, the statistical distributions at ground, calculated by applying the proposed procedure, are used to calculate the indirect‐lightning performances of an overhead line above an ideal and a lossy ground. The results are also compared with those obtained using the original distributions of lightning current parameters, i.e. by neglecting the bias introduced in the distributions by the presence of the instrumented tower, and a significant difference is found.