Alexandre Piantini

A Scale Model for the Study of the LEMP Response of Complex Power Distribution Networks

This paper deals with scale models of power distribution systems for the study of lightning induced voltages on overhead lines. The scale model technique is useful for the investigation of situations which are prohibitively complex to be treated theoretically. For instance, urban distribution networks are usually characterized not only by complex topologies but also by the presence of nearby buildings, whose influence on the lightning induced effects can be successfully evaluated by means of reduced models. The paper first describes the scale model implemented for such a purpose at the University of Sao Paulo, Sao Paulo, Brazil. It then presents a comparison between the experimental data obtained with the scale model and the computer simulations obtained by using the LIOV-EMTP code, a software tool able of calculating lightning-induced electromagnetic transients in distribution systems having complex configurations. Finally, the paper shows an application of the scale model in the evaluation of lightning induced voltages on distribution networks considering the presence of nearby buildings

Lightning-Induced Voltages on Overhead Lines—Application of the Extended Rusck Model

Lightning-induced overvoltages have a considerable impact on the power quality of overhead distribution and telecommunications systems, and various models have been developed for the computation of the electromagnetic transients caused by indirect strokes. The most adequate has been shown to be the one proposed by Agrawal ; the Rusck model can be visualized as a particular case, as both models are equivalent when the lightning channel is perpendicular to the ground plane. In this paper, an extension of the Rusck model that enables the calculation of lightning-induced transients considering flashes to nearby elevated structures and realistic line configurations is tested against data obtained from both natural lightning and scale model experiments. The latter, performed under controlled conditions, can be used also to verify the validity of other coupling models and relevant codes. The so-called Extended Rusck Model, which is shown to be sufficiently accurate, is applied to the analysis of lightning-induced voltages on lines with a shield wire and/or surge arresters. The investigation conducted indicates that the ratio between the peak values of the voltages induced by typical first and subsequent strokes can be either greater or smaller than the unity, depending on the line configuration.

Induced voltages on distribution lines due to lightning discharges on nearby metallic structures

This paper presents a numerical method for the calculation of voltages induced on overhead lines due to lightning discharges striking a metallic structure in its vicinity. The calculation is done from the determination of the electric and magnetic potentials associated with the charges in the return stroke channel and with the currents that propagate in the channel and in the structure. It is shown that in this situation the induced voltages may differ significantly from those originated by lightning discharges direct to the ground. Comparisons between measured and calculated voltage waveforms confirm the validity of the procedure.

An improved model for lightning induced voltages calculations

Overvoltages induced on overhead distribution lines by nearby lightning are responsible for a significant number of supply interruptions, due to their high frequency of occurrence. The importance of the phenomenon has motivated several researches, aiming at a simple and reliable model that can be used for the analysis of the lines performances concerning indirect strokes. This paper presents initially some comparisons between lightning induced voltages recorded in Japan-simultaneously with the associated stroke currents-and those calculated according to some of the existing theories. The results show the consistency of the extended Rusck model (ERM), a method derived from Ruscks theory but with the ability to take into account the finite lengths of line and stroke channel, the occurrence of upward leaders and the effects of lightning incidence to tall structures. Then the effects of these parameters are discussed in order to illustrate the application of the ERM on the analysis of lightning induced voltages.

On the Influence of Stroke Current Propagation Velocity on Lightning Horizontal Electric Fields

This paper discusses the influence of stroke current propagation velocity on the characteristics of lightning horizontal electric fields, considering different types of soil and distances to the stroke location. The MTLE model is adopted for the determination of the current distribution along the return stroke channel, whereas the effect of the finite-ground conductivity is taken into account by using the modified Cooray-Rubinstein approximation. This paper also discusses the effect of the propagation velocity on each of the horizontal electric field components. The results show that the horizontal electric field is strongly influenced by the stroke current propagation velocity even for the case of good conductive ground and observation points relatively close to the stroke location. Regardless of the ground conductivity, the peak value of the static component decreases and the negative peak of the radiation component increases with the propagation velocity. Therefore, for short distances to the lightning channel, the absolute peak value of the horizontal electric field tends to decrease as the velocity increases, while for distances of few kilometers or larger its behavior is just the opposite, i.e., the amplitude increases with the propagation velocity.

Lightning Overvoltages on Rural Distribution Lines

This paper presents information concerning the characteristics of lightning overvoltages on overhead power distribution lines. Discussion on the protection measures against transients caused by both direct and indirect strokes is also presented.

FDTD Computation of Lightning-Induced Voltages on Multiconductor Lines With Surge Arresters and Pole Transformers

In this paper, lightning-induced voltages on multiconductor lines with surge arresters and pole transformers have been computed using the 3-D finite-difference time-domain method. This method uses a subgrid model, in which spatial discretization is fine (cell side length is 0.5 m) in the vicinity of overhead wires and coarse (cell side length is 5 m) in the rest of the computational domain. In the simulations, four-conductor lines with surge arresters and pole transformers are considered. The 1-cm-radius overhead conductors are represented by placing a wire having an equivalent radius of about 0.12 m (≈ 0.23 × 0.5 m) in the center of an artificial rectangular prism having a cross-sectional area of 1 m × 1 m (2 cells × 2 cells) and the modified (relative to air) constitutive parameters: lower electric permittivity and higher magnetic permeability. The computed lightning-induced voltage waveforms agree reasonably well with the corresponding ones measured in the small-scale experiment of Piantini et al. (2007).

Analysis of the disruptive effect model for the prediction of the breakdown characteristics of distribution insulators under non-standard lightning impulses

One of the most commonly used methods for predicting the strength of insulation subjected to lightning impulses of non-standard waveshapes is the Disruptive Effect Model, for which there are different procedures for the estimation of the parameters required for its application. This paper aims at analyzing the main methods for the determination of such parameters. The investigation is based on the comparison of the measured and calculated volt-time characteristics of a 15 kV pin-type porcelain insulator considering two short tail impulse waveshapes (1.2 /4 μs and 1.2 /10 μs), as well as the standard 1.2 /50 μs impulse voltage waveshape. The results relative to the positive and negative polarities of the three voltage waveshapes are presented and discussed.

The effectiveness of shield wires in reducing induced voltages from lightning electromagnetic fields

The mechanisms from which lightning overvoltages can be produced on a power line depend on the system voltage. In medium voltage (MV) overhead distribution systems, lightning transients can be originated by either direct or indirect strokes. The main methods that can be adopted to improve the line lightning performance concern the increase of the critical flashover voltage (CFO) of the line structures, the installation of surge arresters, and the use of one or more periodically grounded shield wires. This paper deals with the evaluation of the effectiveness of shield wires in reducing the magnitudes of the surges induced by nearby strokes on MV distribution lines. Such effectiveness depends on the combination of several parameters such as the relative position of the shield wire with respect to the phase conductors, the grounding interval, the ground resistance, the stroke current steepness, and the relative position of the stroke channel with respect to the grounding points. Realistic situations corresponding to typical configurations of a rural distribution line with either an overhead ground wire or a neutral conductor are considered. The analysis is carried out based on both computer simulations and test results obtained from scale model experiments performed under controlled conditions.

Extension of the Rusck Model for Calculating Lightning-Induced Voltages on Overhead Lines Considering the Soil Electrical Parameters

The validity of the Rusck coupling model and its equivalence to the model by Agrawal, Price and Gurbaxani have already been demonstrated for the case of a perfectly conducting ground and a vertical stroke channel. However, in spite of its popularity, the restriction of an infinite soil conductivity imposes a strong limitation on the use of the model for the analysis of realistic situations. In this paper, a procedure is proposed to extend the Ruscks model to the case of a finite ground conductivity so as to enable the calculation of lightning-induced transients on overhead lines taking into account the soil electrical parameters. The validity of the model is demonstrated through comparisons of simulation results with measured lightning-induced voltages and currents obtained from scale model and rocket-triggered lightning experiments.