On the Characterisations of the Impulse Breakdown in High Resistivity Soils by Field Testing

This paper presents experimental results of high-current impulse tests on six ground electrode configurations. A high impulse current generator is employed to inject different magnitudes of current into these rod electrodes, under both positive and negative impulse polarities. The effect of increasing the number of rod electrodes, hence the resistance at DC or steady-state (RDC), on the impulse response of ground electrodes is analysed. From the analysis of the results, it was found that the larger the size of rod electrodes, the less current-dependent Zimpulse becomes. The percentage of reduction of impulse impedance, Zimpulse from its steady state, and RDC values are found to be independent of impulse polarity. However, as the voltage magnitudes were increased, an occurrence of breakdown was seen, with higher breakdown voltage seen in negative impulse polarity in comparison to positive impulse polarity. Relatively, the higher the breakdown voltage is, seen in the ground electrodes subjected to negative polarity, the faster the time to breakdown is.

Multi-Stroke Lightning Interaction with Wiring Harness: Experimental Tests and Modelling

This paper presents the obtained results of experimental tests and modelling of lightning disturbances that were propagated in a model of aircraft cable bundle and caused by multiple lightning return-strokes interactions. The work is a continuation of previous research, which was concerned mainly with the interaction of lightning discharge with a single return-stroke. The section of the cable harness arranged above the metal plate was investigated. In one of its wires, a multiple-stroke current representing indirect lightning effects was injected from an impulse current generator dedicated to avionics immunity tests. Overvoltages induced at the ends of other wires surrounded by a braided shield, as well as the influence of line parameters and shield grounding condition on the shape and level of observed transients, were examined. The computer simulation results match the measurement data with satisfactory accuracy, and therefore, the presented model can be used to estimate indirect lightning effects in the wiring harness of avionics.

Simulation of impulse current generator for testing surge arresters using frequency-dependent models

The object of research is the equivalent circuit of an impulse current generator designed for testing surge arresters. Calculation of the impulse current generator parameters when discharging a capacitor bank to a complex nonlinear load is a difficult task for an analytical solution. Until now, the application of surge arrester frequency-dependent models was limited to the problems of overvoltage computation. Surge arrester frequency-dependent models can predict the residual voltage with high accuracy. This is the reason to consider that surge arrester frequency-dependent models can be used for calculating the main parameters of impulse current generators designed for physical testing of surge arresters. The task of determining the equivalent circuit parameters required for getting a discharge current of a given waveform and amplitude in an impulse current generator scheme with a nonlinear load was solved using circuit simulation. This article presents the results of studying the processes in impulse current generator equivalent circuit. In the circuit a dynamic model of a surge arrester is used as the load model. For this, an equivalent circuit for the discharge path of the impulse current generator was drawn up. The parameters of the circuit elements (including the required number of capacitors and their charging voltage) are determined, which are necessary for getting a discharge current of a given standardized waveform and amplitude. The parameters of the discharge path are determined for surge arresters of three different voltage classes. It was found that the relative error when determining the residual voltage between the terminals of the surge arrester model does not exceed 3 %. The work contributes to the further development of circuit simulation of surge arresters and the expansion of the scope of surge arrester dynamic models. As a result of the research performed, the possibility of using surge arrester frequency-dependent models for determining the discharge current waveform in impulse current generators is shown. The research performed is relevant due to the fact that surge arresters have become a main tool for protecting the insulation of electrical network equipment against external and internal overvoltages

Nondestructive and electromagnetic evaluations of stealth structures damaged by lightning strike

Stealth technology is very important for the survival of military aircraft. A stealth aircraft structure has both electromagnetic and mechanical functions. Lightning can cause failure on both the points. In this study, we claim that the stealth structure should be evaluated nondestructively and electromagnetically, and we propose a method for full-field evaluations of both the functions. First, a radar absorbing structure was designed and fabricated with stealth capability in the X-band. The radar absorbing structure consisted of a carbon nanotube layer (glass/epoxy dispersed with multiwalled carbon nanotubes), a spacer layer (glass/epoxy) and a perfect electrical conductor layer. A lightning test was performed using an impulse current generator according to standard regulations. Then, nondestructive damage and electromagnetic performance evaluations were performed using a pulse-echo laser ultrasonic propagation imager and a scanning free-space measurement system, respectively. The results showed that neither structural damage nor changes in the electromagnetic properties were observed during the two evaluations. In general, the composites were severely damaged by lightning. However, it turned out that the radar absorbing structure with the carbon nanotube layer could prevent serious damage to stealth function as well as material damage owing to the high conductivity of the carbon nanotubes dispersed in its surface layer.