The Impact of Bipolar Lightning Surges on the Power Distribution Cable Networks Mohamed M. Saied Electrical Engineering Department College of Engineering and Petroleum Kuwait University POBox 5969 Kuwait Kuwait saied@eng.kuniv.edu.kw Abstract- This paper addresses the possible excessive electromagnetic stresses of unusual magnitudes and time waveforms that can appear in power distribution cable networks due to bipolar lightning surges. A sample radial cable network is analyzed in order to demonstrate the possible impact of both the surge amplitude and its time wave shape, in terms of its peak current value and rise time, as well as of the network data such as the length and the surge impedance of the cable sections. Both of the transient voltage and current stresses at the different network locations will be considered. Simulation results will be used in order to identify the locations of possible critical disturbances. They also indicate that, unless adequate surge arresters are applied at properly selected network points, potentially dangerous voltage and current stress concentrations can result. I. INTRODUCTION The accurate analysis of the electromagnetic transients in power networks and components is of crucial importance in the planning, design and operation of electric power networks. Proper insulation coordination and overvoltage protection will depend on the networks’ topology, their characterizing circuit parameters as well as the time waveform of the input voltage and/or current stimuli. 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. In an interesting 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 power networks excited by monopolar multi-pulse lightening surges of different pulse numbers, pulse durations and inter-pulse time separation. 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 applies also the lattice diagrams to explain the possible build-up of voltage surges. Nevertheless, no concrete results have been reported on. Reference [5] presents a more detailed and rigorous approach based on circuit analysis to explain the above-mentioned phenomena of resonating surges. The resulting model applies the distributed parameter line representation, in conjunction with the concept of the generalized ABCD two-port circuit constants. This paper is a further step in this direction. It deals with the transient response of the sample radial distribution feeder network depicted in Fig.1 which is excited by a bipolar lightning strike represented by a current source ) (t i s of the waveform shown in Fig.2. The horizontal axis, which starts from zero, indicates the time t expressed as multiples of the surge or wave rise time w τ defined as the time needed for the surge current to change from zero to its negative peak value - max I . The vertical axis gives the current of the lightning surge ) (t i in per unit based on its peak value max I . It is required to investigate the response of this network in terms of the spatial and temporal distributions of the transient voltages and currents. This will help identify and discuss critical conditions and situations that can lead to electromagnetic transient stresses of unusual magnitudes and/or time waveforms. It should be noted, however, that this issue was rather descriptively treated in reference [6] using both the wave approach as well as simulations applying the Electromagnetic Transients Program (EMTP). The possibility and conditions of “voltage quadrupling” was discussed. It was then mentioned that this phenomenon “may explain some of the unknown cable failures”. A mathematical model based on a distributed parameter Laplace-domain analysis will be presented taking into account the parameters of both the waveform of the discharge surge current as well those of the power network. The results of several runs of a Mathematica program will then be discussed.