Performance of Medium Voltage Urban and Rural Distribution Lines Front Lightning Discharges and Induced Surges

15th International Symposium on High Voltage Engineering, Ljubljana Slovenia, 2007


Abstract:

This paper has as objective to present preliminary results of a study of lightning performance for medium voltage distribution networks, submitted to direct and induced lightning overvoltages. In order to define actions to reduce the network rate of failure the main parameters responsible for the increase of the network failure rate are investigate.
In this stage of the study, some simplifications had been considered. However, the result show that is possible to direct the actions for an economic solution of a series of problems, which represents the great majority of the occurrences involving lightning discharges.

Introduction:

Nowadays many actions for the protection of overhead distribution lines are not well defined and normally without any transient performance study. As a result, many of them besides of presenting high costs 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).
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 most 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 even by laboratory tests.
Therefore, the results are not the most satisfactory and do not achieve a suitable rate of cost by benefit.
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 paper considers that the parameter generation of the discharges follows the statistical data proposed by Anderson and Eriksson [3]. The Monte Carlo Method is used to generate the incidence distribution of the discharges and the Electro Geometrical Model for determining 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] IEEE Guide for Improving the lightning performance of electric power overhead distribution lines, IEEE Standard 1410-1997, June 1997;
[3] Anderson R.B., Eriksson A.J., “Lightning parameters for engineering application”, Electra, No. 69, 1980;
[4] 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;
[5] 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;
[6] Grzybowski, S.; Rodriguez-Medina, B. “Striking distance dependence on rod height and impulse polarity: A system identification approach.” VIII SIPDA, São Paulo, November 2005;
[7] Torres, Horacio. “Statistical evaluation of lightning induced overvoltages in distribution lines in the presence of transformers and surge arresters.” VII SIPDA, Curitiba, November 2003.


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