ELECTROMAGNETIC TRANSIENTS ON POWER LINES DUE TO MULTI-PULSE LIGHTNING SURGES MOHAMED M. SAIED * Kuwait University Kuwait. Abstract This paper identifies and discusses critical conditions in a sample power network that can lead to electromagnetic transient stresses of unusual magnitudes and time waveforms. They can be initiated, for example, by atmospheric discharges involving overhead lines, if the surge includes several pulses of repetitive nature, whose frequency of repetition coincides with or close to the natural frequency of the power line. A mathematical model based on distributed parameter analysis is presented taking into account the parameters of both the waveform of the discharge surge current and the sample power network. 1. INTRODUCTION The information resulting from the analysis of the electromagnetic transient is of paramount importance in the planning, design and operation of electric power networks. Effective insulation coordination and overvoltage protection will be primarily affected by the networks’ topology, their characterizing parameters as well as the time waveform of the input voltage and/or current stimuli. Accurate results from analyzing these situations in terms of the expected transient stresses will allow for more effective protective measures and efficient utilization of the network components. For a detailed survey of the different computer-based techniques pertinent to the transient analysis of power networks, the IEEE Tutorial Course [1] should be consulted. Similar to bibliographies found elsewhere, such as [2, 3], considerable attention was given to transient phenomena involving overhead lines and underground cables, as manifested in the relatively large number of investigations dealing with these elements. In an interesting qualitative recent publication, [4], a model based on the theory of microwave resonators is outlined, capable to explain possible accelerated voltage amplification leading to voltage surge resonance conditions within the power networks. It was observed that “ under appropriate boundary conditions, the oscillating voltage stresses are likely to amplify during back and forth reflections”. The descriptive surge amplification model applies also the lattice diagrams to explain the possible build-up of voltage surges. Nevertheless, no concrete results have been reported on. This investigation tries to present a more detailed and rigorous approach based on circuit analysis, in order to explain the above-mentioned phenomena. The resulting model applies the distributed parameter line representation, in conjunction with the concept of the generalized ABCD two-port circuit constants. The suggested procedure takes into consideration the number of the discharge pulses as well as their frequency of repetition. The location of the point (along the line) hit by the lightning stroke is an important parameter affecting both the waveform and the amplitude of the resulting transient stress. * Electrical Engineering Department, College of Engineering and Petroleum, Kuwait University, P.O.Box 5959 Safat, Code 13060, KUWAIT. 21, rue d'Artois, F-75008 Paris http://www.cigre.org Session 2002 © CIGRÉ 33-101