Indirect Lightning Performance Research Articles

Indirect lightning performance of 10-kV overhead distribution lines

The lightning-induced voltage in 10-kV overhead distribution lines was calculated and analyzed using the Agrawal coupling model and second-order finite difference-time domain (FDTD) method. The influence of lightning position on lightning-induced voltage was analyzed using the concept of indirect lightning withstanding levels. To achieve the limiting effect on lightning-induced voltage in 10-kV lines, the installation density of surge arresters should not be less than 1 group per 200–300 m.

The Indirect-Lightning Performance of Overhead Distribution Line Considering the Mixed Ocean–Land Propagation Path

The Indirect-Lightning Performance of Overhead Distribution Line Considering the Mixed Ocean–Land Propagation Path

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.

A Study of Lightning Performance to Multi-grounded System of KEPCO MV and LV Distribution Network

This paper presents the indirect lightning performance evaluation of Korea Electric Power Company (KEPCO) medium voltage (MV) and low voltage (LV) lines. The main topic of this paper is to analyze an effect of the grounding systems on the indirect lightning performance of MV and LV distribution lines. To this end, we define the models of the MV and LV distribution systems for the analysis of distribution line surge overvoltage due to lightning. With reference to the data typically adopted by KEPCO, the research describes and motivates the use of the most suitable models of distribution lines, transformers, and surge arresters (SAs) to be implemented in EMTP like simulation environments. The sensitivity of the lightning performance of the distribution lines to different configuration of MV and LV grounding systems, distance between SAs, as well as presence of overhead ground wires is also analyzed. Regarding overvoltage, both the temporary overvoltage and the surge overvoltage are considered. The presence of SAs at the MV terminals of distribution transformers is also considered.

Influence of the presence of grounded wires on the lightning performance of a medium-voltage line

The paper compares the effect that the shield wire, underbuilt grounded conductor, and surge arresters have on the direct and indirect lightning performance of medium voltage overhead lines and provides its quantitative assessment. The paper focuses on a line configuration characterized by the presence of both shield wire and underbuilt neutral wire. The presence of the grounded shield wire significantly reduces the voltages induced across the insulators. In case surge arresters are installed, the effect of the shield wire is shown to have a lower impact. The environmental shielding on the overall lightning performance is also accounted for by considering the effect of the buildings close to the line that reduce the frequency of direct events and increase the frequency of indirect ones.

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.

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.

Effect of high-resistivity ground on the lightning performance of overhead lines

This paper presents an approximate formula for the peak-value of the lightning overvoltages induced on aerial lines installed over high resistivity ground, which is valid up to 10 kΩ m. The formula is validated by comparing its results with results obtained from more accurate techniques. The formula is then applied in a Monte Carlo code to assess the effect of high-resistivity ground on the lightning performance of distribution lines without grounded neutral conductor. The results show that, for good conducting ground (e.g., 100 Ω m), indirect flashes are relevant for the 100 kV CFO lines, but they are not relevant for the 170 kV CFO lines. For poorly-conducting ground (e.g., 1000 Ω m), indirect flashes are relevant for 170 kV CFO lines, but they are not relevant for the 300 kV CFO lines. Indirect flashes become relevant for the 300 kV CFO lines only for very poor-conducting ground (e.g., above 2000 Ω m). The paper results also show that using a grounded neutral conductor improves significantly the indirect lightning performance of distribution lines.

Implementation of an analytical formulation for LEMP to assess the lightning performance of a distribution line

This paper presents the implementation of an analytical formulation to calculate the lightning electromagnetic pulse (LEMP) assuming a current wave-shape linearly rising with flat top and a transmission Line (TL) return-stroke model. It also describes the development of the expressions for the image dipoles required to calculate the vertical electric field, the azimuthal magnetic field and, specially, the horizontal electric field. The expressions to calculate the contribution of source dipoles were detailed in a previous publication by other authors. The complete formulation is used to calculate electromagnetic fields and lightning-induced voltages on a typical overhead distribution line. The results were compared with traditional formulas to calculate the LEMP (such as Rubinstein’s) and to calculate induced voltages (such as Rusck’s) showing errors below 1%. If a more complex wave shape was used (such as Heidler’s), errors below 5% were found. Additionally, the formula was employed to calculate the flashover rate of a distribution line above a ground with infinite and finite conductivity. Errors less than 5% were found compared to the results obtained in the IEEE 1410 Standard. On the other hand, the computation time required to the assessment of an overhead line indirect lightning performance is reduced by half when the analytical formula is used.

Indirect Lightning Performance of Aerial Distribution Lines Considering the Induced-Voltage Waveform

This paper shows that the wave-shape parameters of lightning-induced voltages (front-time and time-to-half value) are influenced by the ground resistivity, the line length, and the distance between the flash and the line. In general, these parameters increase with the ground resistivity, the line length, and the distance from the flash. The probabilistic distribution of the waveshape parameters are presented, considering different values of line length and ground resistivity. The effect of the induced voltage waveform on the indirect lightning performance of aerial distribution lines is evaluated using the disruptive effect (DE) method as a flashover criterion. The resulting flashover rates differ significantly from those obtained when only the peak value is used as flashover criterion. The use of a correction factor to multiply the line critical flashover when using the peak value as a flashover criterion is investigated.

Assessment and analysis of indirect lightning performance of overhead lines

This paper presents an efficient method for the assessment of the indirect lightning performance of overhead power lines and analyses the influence of some relevant parameters on the flashover rate. The method is based on a formula to calculate the peak value of lightning-induced voltages in overhead lines over a lossy ground, which considers the front-time of the channel-base current. The results of the method are validated by comparison with results available in the literature. The method is then used to investigate the effect of subsequent strokes on the line flashover rate, leading to the conclusion that their contribution is negligible, as long as no correlation is assumed between front-time and peak value of the strokes (first and subsequent). In the following, the method is used to analyze the influence of some parameters on the lightning performance of overhead lines. The results show that the stroke current front-time influence decreases as the soil resistivity increases, and that a higher front-time leads to a lower flashover rate. It is shown that the use of a fixed front-time T=5.63μs for the first strokes leads to results that match well the results obtained from Cigré’s front-time probabilistic distribution. Regarding the return stroke velocity, the results show that, for soils with resistivity higher than 100Ωm, the flashover rate increases as the return stroke velocity increases. The results also show that a relative velocity vr=0.4 leads to flashover rates that match well the results obtained considering some correlations between return stroke velocity and peak current proposed in the literature. The influence of the correlation between current peak value and front-time for first strokes is also analyzed and it is shown that the correlation reduces the flashover rate. It is also shown that considering this correlation for first strokes and not for subsequent strokes increases the contribution of the latter to the flashover rate, especially for good conducting soils.

Indirect-Lightning Performance of Overhead Distribution Networks With Complex Topology

The paper deals with the evaluation of the indirect-lightning performance of overhead distribution networks. The novelty of this contribution is that it takes into account the inherent complexity of distribution networks. These networks are indeed characterized by a plurality of lines (main feeder and laterals) and also by the presence of typical power components (e.g., transformers and surge arresters); they consequently differ considerably from the straight line configuration generally adopted in this type of studies. To accomplish such an evaluation we have extended the general procedure already presented in a previous paper based on the use of the LIOV code along with the Monte Carlo method. The extended procedure combines the advantage of the LIOV-EMTP computer code-that allows the calculation of lightning-induced voltages in complex distribution networks-with a heuristic technique specifically developed and integrated in the Monte Carlo routine in order to reduce the computational effort. The application of the proposed procedure to a set of distribution overhead networks characterized by different topologies, but all of the same length, shows that, in general, the usual single straight-line approach may result into a misestimation of the indirect-lightning performance. The paper also analyzes and discusses the influence of both the line terminations, and the position of the line poles.

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

Estimation of the Statistical Distributions of Lightning Current Parameters at Ground Level From the Data Recorded by Instrumented Towers

This paper describes a procedure based on the Monte Carlo method to obtain the statistical distributions of lightning current parameters at ground level starting from those inferred from experimental data recorded by means of tall instrumented towers. As a matter of fact, it is generally accepted that these distributions are affected by the presence of the tower; lightning current amplitudes, in particular, are biased toward higher values, as the tower ability to attract lightning flashes tends to increase for flashes with larger currents. Concerning the current peak distribution, the obtained results match with those presented in previous studies on the subject; for instance, for the Berger et al. distribution, they provide a median value decrease ranging from 20%-40%, depending on the attractive radius expression adopted in the calculation. The proposed procedure is more general than others presented in the literature for the same purpose. It can be applied, indeed, to whatever model is adopted to represent the exposure of the tower to direct strokes and, further, it allows to quantify the tower effect on the statistical distributions of all lightning current parameters of interest, and not only of the peak value one. The statistical distributions at ground, calculated with the proposed procedure, should be considered for power system insulation coordination studies, chiefly for a more representative and significant evaluation of the indirect lightning performance of distribution lines. The obtained results can also be used to assess the performance of lightning location systems concerning the relevant current statistical distributions.