임펄스전압에 의한 토양의 이온화 특성

Abstract

This paper presents experimental results of ionization development when lightning impulse voltage is applied to the ground electrode in order to analyze the impact of soil ionization phenomena on the transient performance of grounding system. An experimental study on impulse current spreading from coaxial cylindrical electrode filled with test soil were carried out. Dynamic voltage-current characteristics in soil were measured and analyzed during the impulse current. As a result of experiments, electrical properties of grounding electrodes stressed by impulse currents differs significantly from those determined in case of power frequency low current. The soil ionization arises near the ground electrode surface when the electric field intensity reaches the threshold level. A sharp decrease in ground resistance was observed during the impulse current spreading in soil. The time-lag to the peak current corresponds to the soil ionization development. It has been found that the ionization propagation time increases as the magnitude of impulse current increases. The voltage-current characteristic has a loop-like shape attributed to ionization processes which result in increasing current and decreasing voltage. The stronger the ionization occurs, the larger the cross-sectional area of the closed loop.