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

Abdul Wali Abdul Ali,Normiza Mohamad Nor

doi:10.3390/en14092401

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.

Highlights

Resistivity Soils by Field Testing .Effective grounding systems are needed to ensure current is dissipated to the ground effectively, ensuring safety for persons and equipment in the vicinity of electrical installations
From close examination of the current waveforms, it can be seen that current rise times are the lowest in electrodes with low resistance at DC or steady-state (RDC) values, while other electrodes have slower current rise times, indicating the inductive effect can be significant in high RDC values
It was found that the percentage drops of Zimpulse from the resistance of steady state (RDC ) are in a range of 73% to 89%, and these percentages are independent of the RDC values and impulse polarities

Summary

Introduction

Resistivity Soils by Field Testing .Effective grounding systems are needed to ensure current is dissipated to the ground effectively, ensuring safety for persons and equipment in the vicinity of electrical installations. Many published standards [1,2,3,4] on grounding systems have given emphasis to low ground resistance values, to provide an effective path for currents to ground at power frequency and transient fault conditions. There are two main parameters that should be considered in order to achieve low ground resistance values: electrode and soil properties. Larger electrode and low resistivity values are preferred in order to obtain the required low resistance values at the power frequency. It was found in several studies [5,6,7,8,9]

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Conclusion