Performance of Medium Voltage Urban and Rural Distribution Lines Against Lightning Discharges and Induced Overvoltages

Ground 2006 - International Conference on Grounding and Earth & 2nd International Conference on Lightning Physics and Effects, Maceió, AL, Brazil, 2006


Abstract:

This work has as objective to present the preliminary results of an analysis study of the performance of medium voltage distribution networks, front direct and induced lightning discharges. Analyzing which are the main problems that cause the biggest influence in the direct discharges to the network, in the way to define actions to reduce them. In this stage of the study, some simplifications had been considered. However, the result shows that is possible to direct the actions for the economic solution of a series of problems, which represents the great majority of the occurrences involving lightning discharges. As first result of this study, it was verified that the majority of the distribution problems were caused by induced surges. As the direct discharges constitute only 3 to 4% of the total amount of the lightning discharges to the ground, analyzed for a period of 100 years in a typical distribution network.

Introduction:

Nowadays many actions for the protection of overhead distribution lines are not well taken and without the necessary study. As a result, many of them besides of presenting high cost are not effective. This study has the purpose of leading to an efficient method for the reduction and mitigation of the effects of the lightning discharges in medium voltage overhead distribution lines.
The lightning discharges are one the main causes of interruptions of medium voltage overhead distribution lines, being the reason of great concern for the utility companies. Its destructive effects frequently extends to equipments and connected installations, with the possibility to cause personal injuries and material damages, beyond economic losses, due to out of income and the possibility of indemnities, penalties and fines applied by ANEEL (National Agency of Electric Energy).
In the majority of Brazil the information of lightning discharges were restricted to isoceraunic maps, these maps were widely used by the utility companies.
With the beginning of the deregulation of the electric energy supply, some actions were been taken by the utilities for the prevention and minimization of the damages associated to the lightning discharges.
However, as the lightning discharges are random events, consequently, difficult to predict, the majority of these actions does not follow a study or a detailed analysis of the problem.
By this way, in the greater part of the cases the actions were taken based on the knowledge of the engineer in charge, or based in rules defined without any effective evidence, by means of studies or by laboratory tests. As a result, the results are not the most satisfactory and do not get the correct order of cost by benefit of these actions.
Among others, the distribution network reliability depends directly on its exposition to the lightning discharges. To determine the exposition level of the line, the designer should know the number of discharges to the ground per unit of area per unit of time.
Once that the atmospheric discharges phenomena are random, this work considers that the parameter generation of the discharges follows the statistical data proposed by Anderson and Eriksson. The Monte Carlo Method is used for the incidence distribution of the discharges and the Electro Geometrical Model for the interception point of the discharge.

References:

[1] NUCCI, Carlo Alberto; PAOLONE, Mario; BORGHETTI, Alberto. Effect of tall-instrumented towers on the statistical distributions of lightning current parameters and its influence on the power system lightning performance assessment. VII SIPDA, Curitiba, November, 2003;
[2] METWALLY, I. A.; HEIDLER, F. H.; NICKEL, R. Computation of collection area and probability of lightning strikes to structures using the Electro geometric model. VIII SIPDA, São Paulo, November 2005;
[3] GRZYBOWSKI, S.; RODRIGUEZ-MEDINA, B. Striking distance dependence on rod height and impulse polarity: A system identification approach. VIII SIPDA, São Paulo, November 2005;
[4] TORRES, Horacio. Statistical evaluation of lightning induced overvoltages in distribution lines in the presence of transformers and surge arresters. VII SIPDA, Curitiba, November 2003;
[5] MARTINEZ, Manuel L. B.; MENDONÇA DOS SANTOS, Pedro H. Induced Voltages in Distribution Networks Study, Guide for Improvement of the Performance of Overhead Distribution Networks Against Lightning Discharges. High Voltage Laboratory of the Federal University of Itajubá, MG, Brazil, March 2004;
[6] IEEE Guide for Improving the lightning performance of electric power overhead distribution lines, IEEE Standard 1410-1997, June 1997;
[7] Anderson R.B., Eriksson A.J., Lightning parameters for engineering application, Electra, No. 69, 1980.


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