Performance of Medium Voltage Overhead Lines Against Lightning- Induced OverVoltages: A Comparative Analysis

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


Abstract:

The aim of this research is to present the results collected from the partnership among AES Sul Utility Company, Federal University of Itajubá and University of Bologna. The data are analyzed concerning the performance of possible projects of medium voltage overhead distribution networks, furthermore detailing the procedures used for the simulations. The resultant performance is presented in terms of expected faults for 100 km of line for a density of discharges to the ground (GDF) of 1 discharge/km²/year. Commentaries on the relative performance and comparisons are presented.

Introduction:

The insulation coordination of medium voltage overhead lines performed by means of statistical methods is based on the calculation of the flashover risk. This last can be estimated when both overvoltage statistical distribution and insulation strength are known.
A method developed at the University of Bologna for the calculation of the statistical distribution of indirect lightning induced voltages on overhead distribution lines is first described, and then applied to the AES Sul 25 kV class standard medium voltage distribution line.
The assessment of indirect-lightning performance of distribution lines involves the accurate modeling of the overvoltages induction mechanism. Additionally, for achieving proper insulation coordination, it is necessary to take into account the presence of protection devices, basically constituted by surge arresters and/or grounded shielding wire.
The consequent complexity of the involved phenomena, and the high number of non-linearities, result in a difficult estimation of induced voltages. For such reasons, in the last years, more accurate models, compared with those proposed in the literature of the first part of the last century, have been presented by Nucci and Rachidi [2-5].
In what follows the statistical procedure, to evaluate the overhead line lightning performance, presented by Nucci and Borghetti [6] are extended by Borghetti, Nucci and Paolone [7-10]. Such a procedure is based on more accurate models, thus allowing more accurate description of the overvoltage induction mechanism of indirect lightning, and on the Monte Carlo statistical method.

References:

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