This paper presents the chaotic pulse train (CPT) waveforms of the vertical electric field generated by lightning observed in Malaysia. Focusing on the position where these electric field changes occur in a number of cloud to ground (CG) flashes, these CPTs were detected in different ways of occurrences, durations, intensities and amplitudes. Seventy-six chaotic pulse trains were found in this study from a sum of 172 CG flash records from three thunderstorm days. The fast field antenna was employed to do the field measurements. As opposed to the typical occurrence of chaotic pulse trains prior to subsequent strokes as reported in the literature, this study has found chaotic pulse trains occurring in different places along the CG electric field waveforms.
The grounding system of a lightning protection scheme is designed basically to avoid arcing and
dangerous step potentials. The grounding impedance of the system varies depending on soil structure and frequency. This paper describes the effect of harmonic impedance (also called frequency dependence of soil) on potential distribution under lightning strike to a metal tower with single grounding path, for different soil types. The results show that the peak value of ground potential rise (GPR) and step voltage (SP) may reach extremely hazardous values even at distances in the order of 90 m from the tower footing, especially when soil resistivity is high. Hence, we emphasise that, in contrast to power grounding, when designing of grounding systems that are meant to handle transient or high frequency currents as well, the frequency dependent soil parameters should be considered to avoid hazardous situations, especially at locations with a high probability of lightning strikes such as metal towers.
Soil plays an important role in ground designing. Engineers normally consider only soil resistivity under normal or steady state condition when designing the grounding system. Under certain circumstances such as lightning, electrical response of the soil will change accordingly and thus, the performance of the grounding system will be affected. The purpose of this study is to investigate the effect of moisture content on the electrical behaviour of sand and clay under high impulse voltage condition. Both soil samples are dried in the oven at 110 ± 5°C to remove the water content until became 0%. The samples are subjected to 30 shots of standard (1.2/50μs) lightning impulse voltage for both positive and negative impulse polarities. This is followed by moistening the samples with 5% amount of water over the volume of the samples. The corresponding V50% for both sand and clay was calculated and the value obtained was converted to standard atmospheric condition. The voltage at breakdown and time to breakdown for each soil sample was analysed a statistical analysis conducted for these two parameters to determine if type of soil and moisture content have an effect on the breakdown voltage. In general, it was found that clay is more efficient in neutralising high impulse voltage than sand likely due to the former’s low resistivity and porosity.