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

Abstract

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.

Keywords

• ground electrodes
• impulse impedance
• breakdown in soil